Referencing lung volume for measurements of respiratory system compliance in infants

We propose a method for measurements of respiratory system compliance (C_m) in spontaneously breathing infants, which circumvents the potential problems introduced by the breathby-breath oscillations in the end-expiratory level, i.e., functional respiratory capacity (FRC). Changes in lung volume (V) and pressure at the airway opening (P_ao) were measured in 10 infants breathing through a face mask. A first brief occlusion was to establish a reference V and the corresponding static P_ao; a second occlusion was done at a different V. within the same expiration, or in the following breath. Both occlusions were sufficiently long for the establishment of a stable P_ao value. From the V difference (Δ, where Δ was at least 20% tidal volume) and the corresponding difference in P_ao (Δ_ao) C_rs was computed and averaged (C_rs[REF.VOL.] = Δ/δ_ao). Although, on average, the results were similar to those obtained by the traditional multiple occlusions technique with linear regression analysis of the P_ao-V data points (C_ao[MOT]), in several infants C_rs[REF.VOL] tended to be slightly higher than C_rs[MOT]. Some possibilities for this discrepancy are discussed. It seems likely that breath-tobreath oscillation in FRC may potentially lower C_rs[MOT] by introducing a bias on the V measurement at low P_ao. We conclude that referencing V for C_rs measurements in spontaneously breathing infants is a simple approach, which does not require linear regression analysis and Circumvents the effects of oscillation in FRC. Pediatr Pulmonol. 1993; 16:248–253. © 1993 Wiley-Liss, Inc.     

Can a difference in chest wall mechanics explain the lower respiratory drive during propofol versus halothane anesthesia in children?

This article extends previous work which suggested that respiratory drive was lower during propofol compared with halothane anesthesia. The aim of this study was to assess simultaneously chest wall motion, measured with respiratory inductive plethysmography (RIP), and respiratory drive measured by P_0.1, the pressure generated during the initial 100 msec of an occluded inspiratory effort. Ten healthy children age 3 to 6 years who presented for a dental restorative procedure that required in excess of 2.5 hours were recruited. Patients were anesthetized with propofol (2.5 mg · kg⁻¹; 15 mg · kg⁻¹ · hr) or halothane (1.25%), in a randomized crossover study design. Following induction of anesthesia, RIP bands were placed at the level of the nipples and the umbilicus for the measurement of rib cage and abdomen excursion, respectively. Flow and airway pressure were measured. A manually operated pneumatic balloon was used for brief airway occlusion. Following a 60-minute washin/out of the anesthetic, the children were removed from mechanical ventilation and spontaneous ventilation was reinstated. The RIP signals were calibrated by the method of simultaneous solution of equations. The phase lag was calculated. During airway occlusion the maximal excursion of the calibrated rib cage trace (R_MAX) was measured; a negative value indicated retraction of the rib cage. Respiratory drive was assessed both at a fixed interval (100 msec) (P_0.1) and fixed proportion (10%) (P_10%) of the occluded inspiratory effort. Significance of differences were assessed with a paired t-test (P-value < 0.05). Thoracoabdominal asynchrony was greater during halothane than propofol anesthesia, as was the amount of rib cage retraction, evidenced by lower values of R_MAX; respiratory drive was higher during halothane than propofol anesthesia, as evidenced by higher values of both P_0.1 and P_10%. We conclude that during halothane anesthesia altered chest wall mechanics may result in a greater respiratory drive than during propofol anesthesia. Pediatr Pulmonol. 1998;26:183–189. © 1998 Wiley-Liss, Inc.     

Resistive and elastic unloading to assist spontaneous breathing does not change functional residual capacity

Resistive and/or elastic unloading (a negative ventilator impedance, otherwise termed proportional assist ventilation) may be a useful means to assist spontaneous breathing. This only applies if the ventilator accurately provides pressure changes at the airway opening (P_ao) proportional to the instantaneous flow and/or volume signal of spontaneous breathing and no significant phase lag. We designed such an infant ventilator, which controls the P_ao, by a negative feedback loop, and superimposes a second positive feedback circuit to generate unloading. To test this mode and the ventilator's accuracy in performing the synchronized pressure changes, we examined the functional residual capacity (FRC). We hypothesized that unloading by itself would not alter FRC because P_ao, should return to a preset baseline at end-expiration, and furthermore, that FRC could be actively altered by changing the baseline. Five anesthetized, tracheotomized, spontaneously breathing rabbits [respiratory system compliance 22.4 ± 4.6 mL/kPa (mean ± SEM)] were exposed to end-expiratory P_ao, levels of 0, 0.2, 0.4, and 0.6 kPa. At each of these levels a period of regular continuous positive airway pressure (CPAP) was alternated with a period of unloading (?40 mL/kPa ventilator compliance combined with ?3 kPa/Us ventilator resistance). FRC measured by a sulfur hexafluoride washout technique was virtually identical on CPAP and during unloading at equal end-expiratory P_ao, (difference, 1.41% ± 0.95%), but FRC increased upon elevation of the end-expiratory P_ao, by 29.4 2 3.6 mL/kPa on CPAP and 30.2 ± 3.2 at unloading (difference NS). We conclude that FRC is not destabilized by unloading, but that during unloading, as during CPAP, it depends on the end-expiratory P_ao. Pediatr Pulmonol. 1993; 16:170–176. © 1993 Wiley-Liss, Inc.     

Lung Tissue Resistance Measured in Saline-Filled Guinea Pig Lungs by Micropuncture

Lung tissue resistance (R_ti) measured in air-filled guinea pig lungs by the alveolar capsule technique was a large part of total lung resistance (R_l), and we wondered whether similar results applied to saline-filled lungs. We used the micropuncture method to measure alveolar pressure (P_alv) in saline-filled lungs of 21 guinea pigs. P_alv and airway opening pressure (P_ao) were measured before and after a sudden interruption of flow during an inflation or deflation maneuver. On stopping flow, there was an immediate large change in P_ao followed by a smaller slower change in P_ao. P_alv was nearly constant immediately after flow interruption but followed the slower change in P_ao. The initial change in P_ao on flow interruption was interpreted as the resistive pressure loss in the airways. The small change in P_ao and P_alv was interpreted as the pressure loss caused by tissue stress adaptation. Airway resistance (R_aw) and R_ti were obtained by dividing the pressure losses by the flow before the interruption. R_l was the sum of R_aw and R_ti. The calcium blocker nifedipine reduced both R_aw and R_ti and abolished the difference in R_ti between inflation and deflation. Values of R_ti were 10–29% of R_l. However, with correction for viscosity, R_ti predicted in air-filled lungs would dominate R_l. Accepted for publication: 21 February 1997     

Pleural pressure measured in the zone of apposition of diaphragm to rib cage in rabbits

In 10 anesthetized adult rabbits, we studied the effect of spontaneous breathing and positive pressure ventilation on pleural pressure on the costal lung surface (P_pl) and in the zone of apposition of the rib cage to the diaphragm (P_app). P_pl and P_app were measured by rib capsules installed in the 5th or 6th rib and 11th or 12th rib, respectively. Esophageal (P_es) and gastric (P_ga) pressures were measured with air-filled balloons. At end expiration (functional residual capacity), P_pl was subatmospheric (–2.5 ± 1.4 cm H₂O), decreased during spontaneous inspiration, and was in phase with P_es. In contrast, P_app was above atmospheric pressure (2.1 ± 1.8 cm H₂O), increased during inspiration, and was in phase with P_ga. P_app lagged P_pl by 180° during spontaneous inspiration but was in phase with P_pl during mechanical ventilation. Changes in P_pl (P_pl) during inspiration were greater in magnitude than either P_app or P_ga. Changes in transdiaphragmatic pressure in the zone of apposition (P_ga - P_app) were near zero (–0.4 ± 0.3 cm H₂O), much smaller in magnitude than those (P_ga - P_pl) associated with the lung (3.0 ± 1.5 cm H₂O). These results are consistent with the concept that during breathing, abdominal pressure is transmitted to the zone of apposition of the rib cage to the abdomen. During spontaneous breathing at rest, the pleural space in the zone of apposition is mechanically independent of the pleural space associated with the lung. Offprint requests to: Stephen J. Lai-Fook     

Rib cage mobility in pectus excavatum

Pectus excavatum is generally regarded as a cosmetic deformity; however, some children with pectus excavatum complain of chest pain and exercise limitation. Physiologic studies sometimes show mild restrictive changes and suggest an increased oxygen cost of breathing. Limitation of rib cage mobility related to the deformity may explain these findings. If rib cage mobility is limited, the ability of the actively inspiring rib cage to lower abdominal pressure would be decreased. If this were so, increased swings in abdominal pressure would be seen during the respiratory cycle, especially at times of stress such as during exercise. To test the hypothesis that pectus excavatum is associated with decreased rib cage mobility, we studied 11 patients with pectus excavatum and 11 control subjects. Four control subjects were also studied with rib cage mobility restricted by chest wall strapping sufficient to decrease vital capacity by 5, 10, and 40%. Gastric pressure was measured using balloon catheters and was used as an index of abdominal pressure. Flow at the mouth was recorded and integrated to give volume. Measurements were made at rest, immediately after exercise, and during graded voluntary inspiration to total lung capacity. Gastric pressure was related to tidal volume, and pressure-volume loops were constructed. There were no differences in abdominal pressure swings during respiration between the patients with pectus excavatum and the control subjects. Both groups showed moderate increase in gastric pressure during inspiration at rest and smaller increases or even decreases in abdominal pressure at end inspiration after exercise and at total lung capacity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bilateral diaphragmatic paralysis with hypercapnic respiratory failure: A physiologic assessment

Bilateral diaphragmatic paralysis was suspected in a patient presenting with hypercapnic respiratory failure who exhibited paradoxic (i.e., inward) abdominal movement on inspiration during tidal breathing in the supine posture; no paradoxic abdominal motion was observed at the bedside with the patient upright. Transdiaphragmatic pressure measurements established the diagnosis of diaphragmatic paralysis, although 20 cm H₂O pressure developed across the diaphragm during the latter part of a forced expiration, presumably due to the development of passive tension in the diaphragm as it was stretched near residual volume. Analysis of the relative motion of the rib cage and abdomen during breathing by the use of magnetometers confirmed the presence of abdominal paradox throughout the breathing cycle when the patient was supine, and established that paradoxic motion of the abdomen also occurred when the patient was in the erect posture but only in the latter half of inspiration. Our findings confirm that the use of transdiaphragmatic pressure measurements and magnetometry will help to quantify diaphragmatic function, that passive tension develops in the paralyzed diaphragm near residual volume and should not be confused with active contraction, and that paradoxic motion of the abdomen may be masked from the clinician when the patient is erect.     

Partitioning of alterations in pulmonary mechanics due to vascular engorgement in piglets

The aim of our study was to determine the effects of pulmonary vascular engorgement on airways and pulmonary tissues in juvenile animals before and after methacholine (Mch)-induced changes in lung function. Five anesthetized, paralyzed, and thoracotomized piglets were studied before and during pulmonary vascular engorgement, induced by inflating a left atrial balloon catheter and by calculating respiratory mechanics from measurements of airway opening (P_ao) and alveolar pressures (P_A), respiratory flow (V′), and volume (V) recorded during mechanical ventilation, using the multilinear regression technique. A maximal increase of 15 mmHg in pulmonary artery pressure (P_pa) resulted in a mean increase in total lung elastance (E_L) of 28.6% and in total lung resistance (R_L) of 14.9%. Mch increased E_L by 21.7% and R_L by 29.0%. Inflation of the left atrial balloon with an associated increase in P_pa by 15 mmHg in the presence of Mch resulted in an increase in E_L by a further 12.4% (to 135.4% of baseline) and in R_L by a further 9.0% (to 139.5% of baseline). The change in R_L was associated with a qualitatively similar change in both tissue resistance (V_ti) and airway resistance (R_aw) before and after Mch-induced changes in lung function. We conclude that increasing pulmonary vascular pressures, by increasing left artial pressure, alters lung function in juvenile animals by altering the mechanical properties of both airways and lung tissues. The methods used in the present study allow a direct assessment of the site of action of vascular engorgement in the lungs and provide a useful model for studying this phenomenon further. Pediatr. Pulmonol. 1998; 25:45–51. © 1998 Wiley-Liss, Inc.     

Toluene diisocyanate induction of airway hyperresponsiveness at the threshold limit value (10 ppb) in rabbits

Induction of acute lung injury and the development of airway hyperresponsiveness (AHR) by toluene diisocyanate (TDI) exposure was studied in a new rabbit model of occupational lung diseases. TDI in the range of the threshold limit value (TLV) of 10 ppb, as well as at 5 and 30 ppb, administered four times over period of 1 h to three groups of eight rabbits, did not significantly alter airway resistance (R_I), dynamic elastance (E_dyn), slope of inspiratory pressure generation (P_es/t_I), arterial pressure (P_a) or aterial blood gas tensions (P_aO₂, P_aCO₂). Airway responsiveness (AR) to aerosols of 2% acetylcholine (ACH) was measured before and after each TDI exposure. After TDI inhalation of 10 ppb over 4 h, the amplitude of the ACH-induced airway constrictor response indicated by the changes in E_dyn rose significantly to almost twice the control response value (p < 0.005). Similar changes in the amplitude of R_I and in the slope of P_es/t_I were obtained. After inhalation of 5 ppb TDI, no changes in airway reactivity were observed. The responses of respiratory mechanical parameters to ACH rose to three to four times the control responses after exposure to 30 ppb TDI. In a control group of eight animals not undergoing TDI exposure, no significant changes of respiratory responses were obtained after inhalation of 0.2% ACH for 1 min. In summary, TDI atmospheres in the range of TLV increased AR to ACH within 4 h of exposure in this rabbit model. This augmented AR may indicate an increased risk for the development of isocyanate-induced obstructive lung diseases.Offprint requests to: Dr. rer. nat. Wolfgang Marek     

Comparison of central and peripheral airway involvement before and during methacholine, mannitol and eucapnic hyperventilation challenges in mild asthmatics

Introduction: Testing for airway hyperresponsiveness with indirect stimuli as exercise or mannitol has been proposed to better reflect underlying airway inflammation, as compared with methacholine (MCh), believed to act directly on airway smooth muscle cells. Objective: To investigate whether different direct and indirect stimuli induces different patterns of obstruction, recorded as central and peripheral resistance, and to see whether baseline resistance could predict a positive response to direct or indirect provocation. Methods: Thirty‐four mild asthmatics and 15 controls underwent MCh, mannitol and eucapnic voluntary hyperventilation (EVH) challenge tests. The response was evaluated with spirometry and impulse oscillometry (IOS). Results: Twenty‐three out of 34 asthmatics were positive to either EVH (22) or mannitol (13). Those positive to mannitol had a significant increased baseline value of IOS parameters such as ΔR5‐R20 and AX. Twelve of the asthmatics had a 10% fall or more in forced expiratory volume in 1 s (FEV₁) in all three challenge tests. However, the response pattern measured by IOS did not differ between the tests. When the limit for a positive mannitol provocation was set to 10% fall in FEV₁, 16 out of 19 mannitol‐positive patients were also positive to EVH. Conclusion: Even in mild asthmatics, a substantial number had a positive indirect test. Mannitol FEV₁ provocative dose to decrease FEV₁ by 10% from baseline (PD10) was closely associated to EVH10%. No difference in bronchoconstrictive pattern could be seen between the different provocation tests, but those positive to mannitol had more peripheral airway involvement at baseline. This supports the idea that peripheral airway involvement is an important predictor of asthma airway reactivity. Please cite this paper as: Aronsson D, Tufvesson E, Bjermer L. Comparison of central and peripheral airway involvement before and during methacholine, mannitol and eucapnic hyperventilation challenges in mild asthmatics. Clin Respir J 2011; 5: 10–18.     

Ventilation techniques to minimize circulatory depression in rabbits with surfactant deficient lungs

Changes in aortic blood flow were measured in rabbits with both normal and surfactant depleted lungs in order to elucidate the effect of different modes of ventilation on the circulation while optimizing arterial oxygenation (P_ao2). Conventional mechanical ventilation (CMV), reversed inspiratory to expiratory ratio of CMV (IRV), high frequency positive pressure ventilation (HFV), and high frequency oscillation (HFO) were used. Normocapnia was maintained throughout during different modes of ventilation. In normal lungs the aortic blood flow during IRV was significantly lower with similar levels of P_aO2 compared with CMV, HFV, and HFO. In lavaged lungs, without positive end-expiratory pressure (PEEP), the aortic blood flow during CMV was significantly higher than with other modes of ventilation. When 10 cm H₂O of PEEP was applied, the P_ao2 increased maximally to normal values at all modes of ventilation, but the aortic blood flow was significantly reduced (P < 0.05) during CMV and IRV compared to HFV and HFO. The aortic blood flows at 5 cm H₂O of PEEP were very similar during CMV, HFV, and HFO but significantly reduced during IRV. This study showed that at an optimal arterial oxygenation with higher PEEP levels, maintenance of aortic blood flow was maximal during HFV and HFO. Pediatr Pulmonol. 1994;18:317–322 © Wiley-Liss, Inc.     

Gender Differences in Asthma Management and Quality of Life

Background. Objective assessment of airway function is important in epidemiologic studies of asthma to facilitate comparison between studies. Airway hyperresponsiveness (AHR), peak expiratory flow (PEF) variability, and bronchodilator reversibility (BR) are widely used as markers of airway lability in such studies. Data from a survey of a population sample of adolescents and young adults (n = 609; 288 males), aged 13–23 years, were analyzed to investigate whether AHR, PEF variability, and BR can be used interchangeably as markers of asthma in an epidemiological setting. Methods. Case history, including self-reported and doctor-diagnosed asthma, smoking habits, and use of asthma medication, was obtained by interview and questionnaire. Lung function, airway responsiveness (positive test: PC₂₀ FEV₁< 16 mg/mL histamine), PEF variability (positive test: amplitude percentage mean > 20%), BR (positive test: ΔFEV₁ [(FEV₁max ? FEV₁min)/FEV₁max) 100]> 10%), blood eosinophil count, and skin prick test reactivity were measured by using standard techniques. Results. The prevalence of a positive test was AHR 16.4%, PEFpos 13.3%, and BRpos 7.2%, respectively; 73.5% of the sample had three negative tests. Among the 74 participants with current self-reported asthma (12.2%), 34 subjects (46%) had more than one positive test. Using AHR as the only objective marker of asthma identified 93% of the participants with current asthma, whereas PEF and BR identified 45% and 10%, respectively. Confining the analysis to participants with only one positive test revealed that 61% of the subjects with isolated AHR had current asthma, whereas none of the subjects with isolated BRpos had asthma, and only one participant with isolated PEFpos had current asthma. Degree of histamine responsiveness was closer associated with other asthma-related factors, including self-reported asthma, use of asthma medication, and level of lung function, than PEF variability and bronchodilator responsiveness. Conclusions. Airway responsiveness to histamine, diurnal peak-flow variability, and bronchodilator reversibility cannot be used interchangeably as objective markers of asthma in epidemiologic studies. On the basis of the present findings, airway hyperresponsiveness to a nonspecific bronchoconstrictor is recommended as the objective marker of asthma-related airway lability.     

Use of specific airway resistance to assess bronchodilator response in children

Background and objective: Changes in specific airway resistance (ΔsRaw) after bronchodilation, as measured by plethysmography and FEV₁, are frequently considered to be interchangeable indices of airway obstruction. However, the baseline relationship between these two indices is weak, and the value of ΔsRaw that best predicts FEV₁ reversibility in children has yet to be determined. The aim of this study was (i) to establish the sRaw cut‐off value that best distinguishes between positive and negative bronchodilator responses, as measured by FEV₁ reversibility; (ii) to determine whether the discrepancy between ΔsRaw and ΔFEV₁ might be explained by independent correlations between ΔFEV₁ and both ΔsRaw (mainly airway obstruction) and ΔFVC (airway closure); and (iii) to assess the effect of height and age on the relationship between ΔsRaw and ΔFEV₁. Methods: A retrospective study was performed in 481 children (median age 10.5 years, range 6.1–17.6) with actual or suspected asthma, for whom sRaw and spirometry data were obtained at baseline and after administration of a bronchodilator. Results: The sRaw cut‐off value that best predicted FEV₁ reversibility was a 42% decrease from baseline (P = 0.0001, area under the curve 0.70, sensitivity 55%, specificity 77%) and was independent of height and age. Changes in FEV₁ were significantly but independently related to ΔsRaw and ΔFVC (index of air trapping) (r = 0.40, P < 0.0001 and r = 0.39, P < 0.0001, respectively). Conclusions: A 42% decrease in sRaw predicted FEV₁ reversibility reasonably well, whereas a smaller decrease in sRaw failed to detect approximately one out of two positive responses detected by FEV₁, with no influence of height or age.     

Frequency responses of infant air-balloon versus liquid-filled catheters for intra-esophageal pressure measurement

Amplitude and phase frequency response characteristics of infant air-balloon catheters (IABC) of differing French gauge (FG) sizes and brands were quantified to determine their suitability for measuring dynamic intra-esophageal pressure (P_es) accurately. Frequency response performances of matching IABC and water-filled catheters (WFC) were also compared using the swept sine wave technique. The maximum respiratory rate within which IABCs could potentially measure P_es within a 5% error limit was calculated (F_RR). Frequency responses of IABCs greater than FG size 5 exhibited underdamped resonant properties, while smaller FG size IABCs exhibited near-critical damping or overdamping. IABCs maintained uniform amplitude frequency responses up to 25 Hz, demonstrating the ability to measure P_es potentially up to 148 breaths/min within a 5% error limit. The frequency response performance of FG size 6 IABCs was similar to that of FG size 10 IABCs. Compared with matching WFCs, the frequency response performance of IABCs was significantly superior, the frequency response variability within IABC samples was lower, and IABC correlation between FG size and F_RR was advantageously lower than for WFCs. F_RR values for differing IABC brands and FG sizes are presented. We conclude that IABCs manufactured to infant-appropriate balloon specifications exhibit significantly superior frequency response characteristics compared with matching WFCs. Measurement accuracy is not improved using IABCs greater than FG size 6. Inexpensive intra-esophageal IABCs are technically suitable for the accurate measurement of dynamic P_es during high-frequency respiratory mechanics encountered during infant artificial ventilation. Pediatr. Pulmonol. 1997; 24:353–363. © 1997 Wiley-Liss, Inc.     

Chest wall configurational changes before and during acute obstructive episodes in asthma

We induced bronchial obstruction in 7 otherwise healthy asthmatic subjects and then measured the degree of airway obstruction and the dimensions of the chest wall including the anteroposterior (AP) diameters of the upper and lower rib cage and the abdomen and the transverse diameter of the lower rib cage. Airway obstruction was accompanied by a pronounced increase in the end-expiratory AP diameter of the upper rib cage in all 7 subjects and of the low lateral rib cage in 3 of the 4 subjects in whom this was measured. Other end-expiratory dimensions showed variable changes. In 6 of 7 subjects, obstruction caused the lower rib cage to become more elliptical in cross section during inspiration; transient inward motion of the lower anterior rib cage during early inspiration was noted. This latter motion coupled with the continuous outward motion of the upper anterior rib cage produced a pronounced rocking motion of the sternum during inspiration. These distortions of the chest cage were maximal when obstruction was most severe and gradually diminished as obstruction resolved. These inspiratory changes in chest cage cross-sectional configuration are similar to those seen in normal subjects who attempt to overcome external resistive loading by the increased use of inspiratory muscles; the end-expiratory configuration in asthma indicates an increase in functional residual capacity, which is actively maintained. Multiple degrees of freedom of motion of the chest cage exist during obstructive episodes. Estimates of volume change from measurements of rib cage cross-sectional area and abdominal diameter should be made with caution.     

Pressure‐wire based assessment of microvascular resistance using calibrated upstream balloon obstruction

Objectives : We assess microvascular integrity as a marker of myocardial viability after coronary stenting, using only a pressure guidewire. Background : Microvascular integrity generally is not assessed using pressure‐only guidewires because the transducer lies upstream of microvasculature. We partially inflate a balloon inside a coronary stent to achieve a specific normalized pressure drop at rest (distal coronary/aortic pressure = 0.8) and then infuse a vasodilator, to render the wire sensitive to microvascular function. We hypothesize that the further decline in pressure (ΔFFR_0.8) predicts MRI myocardial viability. Methods : We studied 29 subjects with acute coronary syndrome including myocardial infarction. After successful culprit stenting, the resting coronary/aortic pressure was set to 0.8 using temporary balloon obstruction. ΔFFR_0.8 was defined as 0.8‐(distal coronary/aortic pressures) during adenosine‐induced hyperemia. The average transmural extent of infarction was defined as the average area of MRI late gadolinium enhancement (after 2.8 ± 1.5 days) divided by the corresponding full thickness of the gadolinium enhanced sector in short axis slices, and was compared with ΔFFR_0.8. Results : ΔFFR_0.8 corresponded inversely and linearly with the average transmural extent of infarction (r² = 0.65, P < 0.001). We found that a transmural extent of infarction of 0.50 corresponded to a ΔFFR_0.8 threshold of 0.1, and had high sensitivity and specificity (100% and 94.4%, respectively). Conclusions : Using only an upstream pressure‐sensitive guidewire and a partially obstructing balloon during pharmacologic hyperemia, we were able to predict MRI myocardial viability with high accuracy after relief of epicardial stenosis. With further validation, this may prove a useful clinical prognostic tool after percutaneous intervention. © 2011 Wiley Periodicals, Inc.     

Assessment of left ventricular end-systolic elastance from aortic pressure-left ventricular volume relations

The left ventricular (LV) end-systolic pressure–volume relation (ESPVR) is a load-insensitive method for evaluating LV contractility, which needs invasive measurement. Some noninvasive methods substitute peak aortic pressure (P _S) for end-systolic LV pressure by assuming there is no difference between these pressures. However, this assumption has not been directly validated. With conductance catheter and dual micromanometers, ESPVRs and the slope (Ees_LV) were constructed from simultaneous LV pressures (LVP) and volumes, aortic pressures (AOP) and LV volumes (Ees_AO), and P _S and LV end-ejection volumes (V _EE) (Ees_PP-EEV) during preload reduction in 50 subjects. The ratio of steady-state P _S over V _EE (P _S/V _EE) was also checked. AOP and LVP displayed differences of 11 ± 6 and −30 ± 12 mmHg at the onset and end-ejection, respectively, and −2 ± 4 mmHg at end-systole. Ees_AO and Ees_LV were nearly identical: Ees_AO = 0.97 ×Ees_LV + 0.05, r ² = 0.99. Ees_PP-EEV correlated with Ees_LV (Ees_PP-EEV = 0.57 ×Ees_LV + 0.61, r ² = 0.46) but with much more scatter. P _S/V _EE correlated worst with Ees_LV. Central AOP can be substituted for LVP to derive Ees_LV. Other estimation methods yield weaker and poor correlations to directly measured Ees. Received: August 17, 2001 / Accepted: December 22, 2001     

The interaction between the diaphragm, intercostal/accessory muscles of inspiration and the rib cage

During Mueller maneuvers (MM), the volume change of rib cage, delta Vrc, and abdomen, delta Vab, are equal and opposite. Thus delta Vrc = -delta Vab. Substituting delta Prc.Crc for delta Vrc and delta Pab.Cab for delta Vab yields: delta Prc = - delta Pab.Cab/Crc, where delta Prc, delta Pab, Crc and Cab are applied pressures and compliances of rib cage and abdomen respectively. MM performed solely with the diaphragm permits calculations of Prc in terms of observed changes in Pab and pleural pressure, Ppl. Three trained subjects performed MM with no evidence of inspiratory intercostal or abdominal muscle contraction. During the diaphragmatic MM delta Pab was positive and delta Prc negative. The magnitude of delta Prc/delta Pab was 2-6 times greater than that of delta Ppl/delta Pab. We conclude that neither Pab nor Ppl by themselves displace the relaxed rib cage during Mueller maneuvers. A model in which the diaphragm acts both in parallel and in series with the rib cage, and in which Prc is the sum of Pab and a pressure lying between Pab and Ppl explains these results as well as the hypothesis that Pab displaces the relaxed rib cage during quiet breathing.     

Atopic sensitization to common allergens without symptoms or signs of airway disorders does not increase exhaled nitric oxide

Background: Elevated fractional exhaled nitric oxide (FENO) associates positively with symptomatic atopy among asthmatics and in the general population. It is, however, unclear whether sensitization to common allergens per se– as verified with positive skin prick tests – affects FENO in healthy individuals. Objective: The aim of this study was to examine the association between FENO and sensitization to common allergens in healthy nonsmoking adults with no signs or symptoms of airway disorders. Methods: FENO measurements (flow rate: 50 mL/s), skin prick tests to common inhalant allergens, structured interviews, spirometry, bronchodilatation tests and bronchial histamine challenges were performed on a randomly selected population of 248 subjects. Seventy‐three of them (29%) were nonsmoking asymptomatic adults with no history of asthma, persistent or recurrent upper or lower airway symptoms and no signs of airway disorders in the tests listed above. Results: FENO concentrations were similar in skin prick test positive (n = 32) and negative (n = 41) healthy subjects, with median values of 13.2 and 15.5 ppb, respectively (P = 0.304). No correlation appeared between FENO and the number of positive reactions (r = ?0.138; P = 0.244), or the total sum of wheal diameters (r = ?0.135; P = 0.254). The nonparametric one‐tailed 95% upper limits of FENO among skin prick positive and negative healthy nonsmoking subjects were 29 and 31 ppb, respectively. Conclusions: Atopic constitution defined as positive skin prick test results does not increase FENO in healthy nonsmoking adults with no signs or symptoms of airway disorders. This suggests that same reference ranges for FENO can be applied to both skin prick test positive and negative subjects. Please cite this paper as: Rouhos A, Kainu A, Karjalainen J, Lindqvist A, Piirilä P, Sarna S, Haahtela T and Sovijärvi ARA. Atopic sensitization to common allergens without symptoms or signs of airway disorders does not increase exhaled nitric oxide. The Clinical Respiratory Journal 2008; 2: 141–148.     

Ventilatory and respiratory muscle responses to hypercapnia in patients with paraplegia

To evaluate ventilatory and respiratory muscle responses to hypercapnia in patients with paraplegia with paralysis of abdominal muscles, we studied seven patients with complete transection of the midthoracic cord (Th6-Th7) and six normal subjects. Minute ventilation (V E) and mean inspiratory flow responses to hypercapnia were similar in normal subjects and patients with paraplegia, but in the latter, at any given level of end-tidal CO(2) partial pressure (PET(CO(2))), tidal volume (VT) was reduced and frequency was increased. In normal subjects during hypercapnia, end-expiratory transpulmonary pressure (PL) and abdominal volume at end expiration decreased markedly, whereas end-expiratory volume of the rib cage (Vrc,E) remained constant, suggesting progressive recruitment of abdominal muscles. In patients with paraplegia compared to normal subjects the decrease in end-expiratory PL was reduced, and it was associated with a decrease in Vrc,E, suggesting recruitment of rib cage expiratory muscles. For a PET(CO(2)) of 70 mm Hg the estimated expiratory muscle contribution to VT was 10.3 and 28.4% (p < 0.02) in patients with paraplegia and normal subjects, respectively. We conclude that the V E-CO(2) relationship is preserved in patients with paraplegia with the development of a rapid and shallow pattern of breathing. This suggests that expiratory muscle paralysis elicits adaptation of the ventilatory control system similar to that observed in patients with generalized respiratory muscle weakness.