Comparison of impedance minute ventilation and direct measured minute ventilation in a rate adaptive pacemaker

Respiration rate (RR) and minute ventilation (MV) provide important clinical information on the state of the patient. This study evaluated the accuracy of determining these using a pacemaker impedance sensor. In 20 patients who were previously implanted with a Guidant PULSAR MAX group of pacemakers, the telemetered impedance sensor waveform was recorded simultaneously with direct volume respiration waveforms as measured by a pneumatometer. Patients underwent 30 minutes of breathing tests while supine and standing, and a 10-minute ergonometer bicycle exercise test at a workload of 50 W. Breathing tests included regular and rapid-shallow breathing sequences. RR was determined by a computerized algorithm, from impedance and respiration signals. The mean RR by impedance was 21.3 +/- 7.7 breaths/min, by direct volume was 21.1 +/- 7.6 breaths/min, range 7-66, the mean difference of RR measured by the impedance sensor, as compared with the true measurement, being 0.2 +/- 2.1 breaths/min. During the entire exercise, the mean correlation coefficient between impedance (iMV) and direct measured MV was 0.96 +/- 0.03, slope 0.13 +/- 0.05 L/Omega and range 0.07-0.26 L/Omega. Bland-Altman limits of agreement were +/- 4.6 L/min for MV versus iMV with each patient calibrated separately. The correlation coefficient for iMV versus MV over the entire 10 minutes of exercise, including the initial 4 minutes of exercise, was 0.99. The transthoracic impedance sensor of an implanted pacemaker can accurately detect respiration parameters. There was a large variation between subjects in the iMV versus MV slope during a bicycle exercise test, whereas for each subject, the slope was stable during submaximal bicycle exercise.     

Clinical trial of umbilical artery Doppler waveform quality indices.

The ability of two Doppler waveform quality indices to discriminate between high- and low-quality waveforms was tested using 427 sets of umbilical artery Doppler waveforms from patients. The waveforms had been acquired using a 4-MHz continuous-wave Doppler unit. The quality indices (QI) were based on an assessment of the degree of noise of the maximum frequency envelope of the waveforms, and were first a correlation between successive waveform envelopes (QI1), and, second, a sum of local linearity measures (QI2). The sets of waveforms were graded subjectively according to the clarity of the outline of the waveforms, the degree of interference in the region of the spectrum above the outline, and in terms of the degree of variability caused by fetal breathing. At 90% sensitivity for detection of low-quality waveforms according to a high envelope clarity score, the specificities were 68.2% and 52.7%, respectively, for QI1 and QI2. QI1 was independent from pulsatility index and waveform length, but showed strong dependence on fetal breathing. QI2 showed strong independence from pulsatility and fetal breathing and reasonable independence from waveform length. Both QI1 and QI2 performed poorly when there was a large degree of noise in the region of the spectrum above the envelope; however, this poor performance was often related to the inability of the maximum frequency follower to estimate correctly the maximum frequency envelope in those conditions so that the high waveform quality values reflected the erroneous calculation of pulsatility index in those cases.     

Comparison of the oxygen cost of breathing exercises and spontaneous breathing in patients with stable chronic obstructive pulmonary disease

BACKGROUND AND PURPOSE: The oxygen demand of breathing exercises and the clinical implications have not been studied in detail. In this study, the oxygen cost of 3 common breathing exercises believed to reduce oxygen cost (ie, work of breathing) was compared with that of spontaneous breathing in patients with chronic obstructive pulmonary disease (COPD). SUBJECTS: Thirty subjects with stable, moderately severe COPD participated. METHODS: Oxygen consumption (VO2) and respiratory rate (RR) during spontaneous breathing at rest (SB) were recorded for 10 minutes. Subjects then performed 3 breathing exercises in random order, with a rest between exercises: diaphragmatic breathing (DB), pursed-lip breathing (PLB), and a combination of DB and PLB (CB). Oxygen consumption and RR were measured. RESULTS: Mean VO2 ( SD) was lower during the breathing exercises (165.8 +/- 22.3 mL O2/min for DB, 164.8 +/- 20.9 mL O2/min for PLB, and 167.7 +/- 20.7 mL O2/min for CB) compared with SB (174.5 +/- 25.2 mL O2/min). Correspondingly, mean RR (+/- SD) was higher during SB (17.3 +/- 4.23 breaths/min), followed by DB (15.0 +/- 4.32 breaths/min), PLB (12.8 +/- 3.53 breaths/min), and CB (11.2 +/- 2.7 breaths/min). DISCUSSION AND CONCLUSION: Given that patients do not spontaneously adopt the breathing pattern with the least O2 and the lowest RR, the results suggest that determinants of the breathing pattern other than metabolic demand warrant being a primary focus in patients with COPD.     

An investigation of simulated umbilical artery Doppler waveforms. II. A comparison of three Doppler waveform quality indices

Three Doppler waveform quality indices based upon assessment of the noise of the maximum frequency envelope of simulated umbilical artery waveforms were investigated. These indices were: an estimate of the correlation between successive waveforms (QI1), a local linearity measure (QI2) and a ratio of two regions of the Fourier transform amplitude spectrum of the maximum frequency envelope (QI3). Simulated umbilical artery waveforms were acquired from a physiological flow phantom. A test population was used consisting of a large number of waveforms where one of three physical variables had been adjusted to produce waveforms of varying quality. These three physical variables were: beam-vessel angle, beam-vessel axial misalignment and attenuator thickness. For this group of waveforms the accuracy of estimation of the maximum frequency envelope and pulsatility index (PI) were known. All three quality indices gave good separation of high- and low-quality waveforms based upon threshold values of the accuracy of PI and maximum frequency envelope. The dependence of each quality index on fetal breathing, waveform length and waveform pulsatility was investigated. QI2, the local linearity measure, showed most promise in its independence from these variables.     

Comparison of the effects of heat and moisture exchangers and heated humidifiers on ventilation and gas exchange during non-invasive ventilation

OBJECTIVE: To compare the short-term effects of a heat and moisture exchanger (HME) and a heated humidifier (HH) during non-invasive ventilation (NIV). DESIGN: Prospective, clinical investigation. SETTING: Intensive care unit of a university hospital. PATIENTS: Twenty-four patients with acute respiratory failure (ARF). INTERVENTION: Each patient was studied with a HME and a HH in a random order during two consecutive 20min periods of NIV. MEASUREMENTS AND RESULTS: Respiratory rate (RR), expiratory tidal volume (VTe) and expiratory minute ventilation (VE) were measured during the last 5 min of each period and blood gases were measured. Mean pressure support and positive end-expiratory pressure levels were, respectively, 15+/-4 and 6+/-2 cmH(2)O. VE was significantly greater with HME than with HH (14.8+/-4.8 vs 13.2+/-4.3 l/min; p<0.001). This increase in VE was the result of a greater RR for HME than for HH (26.5+/-10.6 vs 24.1+/-9.8 breaths/min; p=0.002), whereas the VT for HME was similar to that for HH (674+/-156 vs 643+/-148 ml; p=0.09). Arterial partial pressure of carbon dioxide (PaCO(2)) was significantly higher with a HME than with a HH (43.4+/-8.9 vs 40.8+/-8.2 mmHg; p<0.005), without significantly changing oxygenation. CONCLUSION: During NIV the increased dead space of a HME can negatively affect ventilatory function and gas exchange. The effect of HME dead space may decrease efficiency of NIV in patients with ARF.     

Cardiorespiratory effects of naloxone in children

BACKGROUND: Data on the cardiorespiratory changes and complications following administration of naloxone in children are limited. OBJECTIVE: To evaluate the cardiorespiratory changes and complications following naloxone treatment in children. METHODS: The maximal changes in respiratory rate (RR), heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure, and any complications within 1 and 2 hours following naloxone were tabulated. RESULTS: One hundred ninety-five children received naloxone over 3 years. The mean +/- SD age was 9.7 +/- 6 years. The total doses of naloxone ranged from 0.01 to 7 mg (0.001-0.5 mg/kg body weight), with a median dose of 0.1 mg. Group 1 patients consisted of 116 (60%) children who were postoperative and had been given naloxone by an anesthesiologist; group 2 patients consisted of 79 (40%) children who received naloxone in the emergency department or pediatric intensive care unit. Patients in group 1 were older: 10.6 +/- 5.3 versus 8.2 +/- 6.7 years (p < 0.006), but received significantly lower doses of naloxone (0.09 +/- 0.2 vs. 1.1 +/- 0.76 mg; p < 0.001). When the entire cohort was evaluated, a significant increase in RR (15 +/- 7 vs. 21 +/- 8 breaths/min; p < 0.001), HR (102 +/- 29 vs.107 +/- 29 beats/min; p < 0.001), SBP (109 +/- 17 vs. 115 +/- 15 mm Hg; p < 0.001), and DBP (56 +/- 10 vs. 60 +/- 13 mm Hg; p < 0.001) within 1 hour following naloxone was noted. When the 2 groups were compared, only the changes in RR were greater in group 2 patients (6.8 +/- 7.9 vs. 4.7 +/- 5 breaths/min; p < 0.001) following naloxone. Systolic hypertension occurred in 33 of 195 (16.9%) of all patients, while diastolic hypertension occurred in 13 (6.6%) of all patients after naloxone. Only the incidence of diastolic hypertension was higher in group 2 compared with group 1 patients following naloxone (16% vs. 2%; p < 0.001). Hypertension resolved spontaneously. One child developed pulmonary edema and required positive pressure ventilation for 22 hours. CONCLUSIONS: Moderate increases in RR, HR, and BP occur after naloxone administration to children, but development of more serious complications is rare.     

Effects of single-hole and cross-cut nipple units on feeding efficiency and physiological parameters in premature infants

The purpose of this study was to compare the amount of total milk intake, feeding time, sucking efficiency, heart rate (HR), respiratory rate (RR), and oxygen saturation (SpO2) of premature infants when fed with either signal-hole or cross-cut nipple units. Twenty stable infants admitted to a level II nursery in a tertiary care center with gestational ages averaging 32.2+/-3.2 wks were enrolled. Subjects had an average postmenstrual age of 34.1+/-1.6 wks, and average body weight of 1996+/-112 gm. A crossover design was used and infants were observed for two consecutive meals separated by a four-hour interval. They were bottle fed with equal feeding amounts using a single-hole and cross-cut nipple administered in random order. Results showed that infants fed with single-hole nipple units took more milk (57.5+/-8.3 ml vs. 51.6+/-9.5 ml, p=.011), had a shorter feeding time per meal (11.5+/-4.9 min vs. 20.9+/-5.0 min, p<.001), and sucked more efficiently (5.8+/-2.5 ml/min vs. 2.7+/-1.0 ml/min, p<.001) compared to those fed through cross-cut nipples. Infants using cross-cut nipple units had a higher RR (44.4+/-4.6 breaths/minutes vs. 40.8+/-4.9 breaths/minutes, p=.002) and SpO2 (96.1+/-1.4% vs. 94.6+/-3.2%, p=.044) than those using single-hole nipples. Oxygen desaturation (SpO2<90% and lasting for longer than 20 sec) and bradycardia were not recorded in either group of infants during feeding. Compared to using cross-cut nipple units, premature infants using single-hole nipple units take more milk and tend to tolerate feedings better. A single-hole nipple may be a choice for physiologically stable bottle-fed premature infants.     

The effect of varying inspiratory flow waveforms on pulmonary mechanics in critically ill patients

Purpose: Ten mechanically ventilated patients were evaluated to determine the effect of three different inspiratory flow patterns on pulmonary mechanics. Materials and Methods: Ten consecutive mechanically ventilated critically ill patients with acute respiratory failure admitted to the intensive care unit were evaluated to assess the effects of decelerating, square, and sine waveforms on pulmonary mechanics. The variables measured were peak airway pressure (PaW), pleural pressure (Ppl), change in peak airway pressure (dPaW), inspiration time/total ventilation cycle time (Vi/Vtot), dynamic compliance (Cdyn), respiratory rate (RR), minute ventilation (Ve), and work of breathing (WOB). Results: The PaW, Ppl, and dPaW (cm H₂O) were significantly lower using the decelerating inspiratory flow waveform (P < .05) compared with sine or square waveform patterns. Ti/Ttot was also lower with the decelerating waveform (P < .05) with better dynamic compliance compared with the other waveforms (P < .10). Conclusions: These results indicate that critically ill mechanically ventilated patients show improved respiratory mechanics with decelerating inspiratory waveform that may have beneficial clinical implication. Copyright © 2000 by W.B. Saunders Company     

Autotriggering caused by cardiogenic oscillation during flow-triggered mechanical ventilation

OBJECTIVES: We noticed that in some patients after cardiac surgery, when flow triggering was used, cardiogenic oscillation might be autotriggering the ventilatory support. In a prospective study, we evaluated the degree of cardiogenic oscillation and the frequency rate of autotriggering. We suspected that autotriggering caused by cardiogenic oscillation was more common than clinically appreciated. DESIGN: Prospective, nonrandomized, clinical study. SETTING: Surgical intensive care unit in a national heart institute. PATIENTS: A total of 104 adult patients were enrolled after cardiac surgery. INTERVENTIONS: During the study period, patients were paralyzed and ventilated with intermittent mandatory ventilation at a rate of 10 breaths/min, pressure support of 10 cm H2O, and flow triggering with a sensitivity of 1 L/min. MEASUREMENTS AND MAIN RESULTS: Because the patients would not be able to breathe spontaneously, we counted pressure-support (PS) breaths as instances of autotriggering. Then, we classified the patients into two groups according to the number of PS breaths: an "AT group" (PS breaths of >5/min) and a "non-AT group" (PS breaths of < or =5/min). If autotriggering occurred, we decreased the sensitivity so autotriggering disappeared (threshold triggering sensitivity). The intensity of cardiogenic oscillation was assessed as the flow and airway pressure at the airway opening. A total of 23 patients (22%) demonstrated more than five autotriggered breaths/min. During mechanical ventilation, the inspiratory flow fluctuation caused by cardiogenic oscillation was significantly greater in the AT group than in the non-AT group (4.67+/-1.26 L/min vs. 2.03+/-0.86 L/min; p<.01). The AT group also showed larger cardiac output, higher ventricular filling pressures, larger heart size, and lower respiratory system resistance than the non-AT group. As the inspiratory flow fluctuation caused by cardiogenic oscillation increased, the level of triggering sensitivity also was increased to avoid autotriggering. In the AT group with 1 L/min of sensitivity, the respiratory rate increased (19.9+/-2.7 vs. 10+/-0 breaths/min, p<.01), Paco2 decreased (30.8+/-4.0 torr [4.11+/-0.36 kPa] vs. 37.6+/-4.3 torr [5.01+/-0.57 kPa]; p < .01), and mean esophageal pressure increased (7.7+/-3.0 vs. 6.9+/-3.0 cm H2O; p<.01) compared with the threshold triggering sensitivity. CONCLUSIONS: Autotriggering caused by cardiogenic oscillation is common in postcardiac surgery patients when flow triggering is used. Autotriggering occurred more often in patients with more dynamic circulation. Autotriggering caused respiratory alkalosis and hyperinflation of the lungs.     

Pulse and Systolic Pressure Variation Assessment in Partially Assisted Ventilatory Support

OBJECTIVE: The use of pulse pressure variation (PPV) and systolic pressure variation (SPV) is possible during controlled ventilation (MV). Even in acute respiratory failure, controlled MV tends to be replaced by assisted ventilatory support. We tested if PPV and SPV during flow triggered synchronized intermittent mechanical ventilation (SIMV) could be as accurate as in controlled MV. METHODS: Prospective case-controlled study. Thirty patients who met criteria of weaning from controlled MV. Twenty minutes pressure support ventilation with 3 min(-1) flow triggered SIMV breathes (10 ml kg(-1)) T1, then three consecutive breaths in controlled MV (respiratory rate 12 min(-1),10 ml kg(-1)) T2. PPV and SPV were measured in T1 and T2. Correlation and Bland-Altman analysis were used to compare respective values of PPV and SPV in the two modes of ventilation. RESULTS: Significant correlations were found between dynamic indices in SIMV during pressure support ventilation and those in controlled MV mode. The mean differences between two measurements were: PPV 0.6+/-2.8% (limit of agreement: -5.0 and 6.2), SPV 0.5+/-2.3 mmHg (limit of agreement: -4.0 and 5.1). CONCLUSIONS: PPV and SPV measured during SIMV fitted with the findings in controlled MV. Dynamic indexes could be accurately monitored in patients breathing with assisted respiratory assistance adding an imposed large enough SIMV breath.     

Influence of respiratory rate on gas trapping during low volume ventilation of patients with acute lung injury

OBJECTIVE: Reduction in tidal volume (Vt) associated with increase in respiratory rate to limit hypercapnia is now proposed in patients with acute lung injury (ALI). The aim of this study was to test whether a high respiratory rate induces significant intrinsic positive end-expiratory pressure (PEEPi) in these patients. DESIGN: Prospective crossover study. SETTING: A medical intensive care unit. INTERVENTIONS AND MEASUREMENTS: Ten consecutive patients fulfilling criteria for severe ALI were ventilated with a 6 ml/kg Vt, a total PEEP level at 13+/-3 cmH(2)O and a plateau pressure kept at 23+/-4 cmH(2)O. The respiratory rate was randomly set below 20 breaths/min (17+/-3 breaths/min) and increased to 30 breaths/min (30+/-3 breaths/min) to compensate for hypercapnia. External PEEP was adjusted to keep the total PEEP and the plateau pressure constant. PEEPi was computed as the difference between total PEEP and external PEEP. The lung volume retained by PEEPi was then measured. RESULTS: Increase in respiratory rate resulted in significantly higher PEEPi (1.3+/-0.4 versus 3.9+/-1.1 cmH(2)O, p<0.01) and trapped volume (70+/-43 versus 244+/-127 ml, p<0.01). External PEEP needed to be reduced from 11.9+/-3.4 to 9.7+/-2.9 cmH(2)O ( p<0.01). PaO(2) was not affected but the alveolar-arterial oxygen tension difference slightly worsened with the high respiratory rate (p<0.05). CONCLUSIONS: An increase in respiratory rate used to avoid Vt reduction-induced hypercapnia may induce substantial gas trapping and PEEPi in patients with ALI.     

Characterization of volumetric flow rate waveforms in the normal internal carotid and vertebral arteries

Knowledge of normal cerebrovascular volumetric flow rate (VFR) dynamics is of interest for establishing baselines, and for providing input data to cerebrovascular model studies. Retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms from the two internal carotid arteries (ICA) and two vertebral arteries (VA) of 17 young, normal volunteers (16M:1F) at rest in a supine posture. After normalizing each waveform to its respective cycle-averaged VFR, the timing and amplitude of feature points from the individual waveforms were averaged together to produce archetypal ICA and VA waveform shapes. Despite significant inter-individual differences in cycle-averaged VFR within the ICA compared to VA (275+/-52 versus 91+/-18 mL min-1), the respective waveform shapes were qualitatively similar overall. The VA waveform shape did, however, exhibit significantly higher amplitudes (e.g., peak:average VFR of 1.78+/-0.30 versus 1.66+/-0.16; p<0.05) and significantly higher variability both between and within subjects. A significant correlation was observed between peak and cycle-averaged VFR, suggesting that the representative waveform shapes presented here-when scaled by an individual's cycle-averaged VFR-may be used to characterize normal ICA and VA flow rate dynamics. This capability may be of particular utility for studies where cerebrovascular flow dynamics are required, but only average flow rates are available.     

An evaluation of the Integrated Pulmonary Index (IPI) for the detection of respiratory events in sedated patients undergoing colonoscopy

The Integrated Pulmonary Index (IPI?) is a new decision making tool calculated from measured end tidal carbon dioxide (etCO(2)), respiratory rate (RR), oxygen saturation (SpO(2)) and pulse rate (PR) using a fuzzy logic model. The aim of this study was to compare prospectively IPI to respiratory adverse events in patients undergoing moderate sedation for colonoscopy. Following ethics committee approval and personal informed consent 51 adult patients undergoing elective colonoscopy were enrolled. Patients received routine care by the endoscopy staff that were blinded to IPI, etCO(2), and RR; whilst a trained senior anesthesiologist observer, not involved in the procedure, collected this data. 'Requires attention' respiratory adverse events (at least 1 min of SpO(2) ≤ 92 % and/or RR ≤ 8 and or 20 % decrease in etCO(2)) and 'requires intervention' respiratory adverse events (at least 1 min of SpO(2) ≤ 85 % and/or RR = 0) were documented by the observer. There were no differences in etCO(2), RR, SpO(2) and PR between 5778 IPI readings ranging from 1 to 10. Low (1-3), medium (4-6) and high (7-10) IPI groups did not differ in RR, SpO(2) and PR, but etCO(2) was higher in the high IPI group (p = 0.0185). Among requires attention events (n = 113) the IPI was high (7-10) in 53.1 %, intermediate (4-6) in 32.7 %, or low (1-3) in 14.2 %. The presented data demonstrate limited agreement between respiratory physiological parameters and the IPI. Further IPI evaluation and validation is indicated mainly for events requiring immediate intervention and in different patient populations including obese patients.     

Increasing respiratory rate to improve CO2 clearance during mechanical ventilation is not a panacea in acute respiratory failure

BACKGROUND: Increasing respiratory rate has recently been proposed to improve CO2 clearance in patients with acute respiratory failure who are receiving mechanical ventilation. However, the efficacy of this strategy may be limited by deadspace ventilation, and it might induce adverse hemodynamic effects related to dynamic hyperinflation. SETTING: An intensive care unit of a university hospital. PATIENTS: We studied 14 patients with acute respiratory failure during the adjustment of ventilator settings on the first day of mechanical ventilation in volume-controlled mode. MEASUREMENTS: After determining the positive end-expiratory pressure that suppresses any intrinsic positive end-expiratory pressure at a respiratory rate of 15 breaths/min, we compared blood gas analysis, respiratory measurements, and Doppler evaluation of right ventricular systolic function by using two different respiratory strategies with the same airway pressure limitation (plateau pressure, < or =25 cm H2O), a low-rate conventional respiratory strategy with a respiratory rate of 15 breaths/min, and a high-rate strategy with a respiratory rate of 30 breaths/min. RESULTS: Compared with the low-rate strategy, the high-rate strategy neither significantly reduced PaCO2 (47 +/- 8 vs. 51 +/- 7 mm Hg with the low-rate strategy) nor significantly improved PaO2 (99 +/- 40 vs. 95 +/- 35 mm Hg with the low-rate strategy). It significantly increased alveolar deadspace to tidal volume ratio (21% +/- 8%, vs. 14% +/- 6% with the low-rate strategy) and produced dynamic hyperinflation, resulting in a substantial intrinsic positive end-expiratory pressure (6.4 +/- 2.7 cm H2O). Right ventricular outflow impedance was increased, resulting in a significant drop in the cardiac index (2.9 +/- 0.6 vs. 3.3 +/- 0.7 L/min/m with the low-rate strategy). CONCLUSION: We conclude that a high respiratory rate strategy during mechanical ventilation in patients with acute respiratory failure did not improve CO2 clearance, produced dynamic hyperinflation, and impaired right ventricular ejection.     

Can Current Minute Ventilation Rate Adaptive Pacemakers Provide Appropriate Chronotropic Response in Pediatric Patients?

Since children have different activity patterns and exercise responses, uncertainty exists as to whether minute ventilation (MV) sensors designed for adults provide adequate chronotropic response in pediatrics. In particular, high respiratory rates (RR > 48 breaths/min), which are characteristic of the ventilatory response to exercise in children, cannot be sensed by MV rate responsive pacemakers. The purpose of this study was to evaluate the MV sensor rate response of the Medtronic Kappa 400 using exercise data from healthy children in a computer simulation of its rate response algorithm. Thirty-eight healthy children, ages 6-14, underwent a treadmill maximal exercise test. Subjects were divided based on body surface area (BSA) and MV rate response parameters were selected. Respiratory rates and tidal volumes were entered into the Kappa 400 rate response algorithm to calculate sensor-driven rates. Intrinsic heart rate (HR), oxygen uptake, and sensor-driven rates were normalized to HR reserve (HRR), metabolic reserve (MR), and sensor-driven reserve to compare across groups. Linear regression analysis among sensor-driven rate reserve, HRR, and MR was performed as described by Wilkoff. The mean slopes (+/- SD) of the relationships between the sensor-driven rate reserve and HRR were 1.06 +/- 0.34, 1.07 +/- 0.28, and 1.01 +/- 0.19 for children with BSA < 1.10 m2, 1.10 < BSA < 1.40 m2, and BSA > 1.40 m2, respectively. High correlations were found between sensor-drive rates and HR responses and between sensor-drive rates and MV throughout exercise. No significant differences were noted between sensor-drive rates and HR using the Wilkoff model. From this study the authors conclude that: (1) MV is a good physiological parameter to control heart rate and (2) simulated sensor-driven rates closely match intrinsic HRs during exercise in healthy children, which supports the appropriateness of clinical validation in pediatric pacemaker patients.     

Effect of ventilatory variables on gas exchange and hemodynamics during total liquid ventilation in a rat model

OBJECTIVES: To investigate the settings necessary to achieve maximum gas exchange and pulmonary function while minimizing effects on cardiovascular hemodynamics during total liquid ventilation with a pressure-limited, time-cycled ventilator in a rat model. DESIGN: Prospective, randomized controlled animal study. SETTING: A university research laboratory. SUBJECTS: Male Sprague-Dawley rats (n = 48). INTERVENTIONS: All animals had a tracheostomy tube designed for total liquid ventilation placed under anesthesia. The carotid artery was cannulated for blood pressure monitoring and for assessing blood gas data. MEASUREMENTS AND MAIN RESULTS: Forty 492 +/- 33 g rats were assigned to one of four inspiratory/expiratory ratio groups (inspiratory/expiratory ratio of 1:2, 1:2.5, 1:3, and 1:4). Total liquid ventilation was performed with a pressure-limited, time-cycled total liquid ventilator. Outcome measures were evaluated as a function of respiratory rate and included tidal volume, maximal alveolar ventilation, inspiratory and expiratory mean arterial pressures, the difference of mean arterial pressure between the inspiratory and expiratory phase, static end-inspiratory/expiratory pressures, Paco(2), Pao(2), tidal volume + approximate expiratory reserve volume, and lung volume-induced suppression of mean arterial pressure. Maximal alveolar ventilation increased and decreased in parabolic fashion as a function of respiratory rate and was maximal at rates of 4.3-6.8 breaths/min and high inspiratory/expiratory ratios that corroborated with optimal levels of Pao(2) and Paco(2). Lung overdistention occurred at high respiratory rates and high inspiratory/expiratory ratios. Deleterious effects were observed on the difference of mean arterial pressure between the inspiratory and expiratory phase during total liquid ventilation at low respiratory rates, apparently due to increased tidal volume, and on suppression of mean arterial pressure at high inspiratory/expiratory ratios and high respiratory rate apparently due to "auto-positive end-expiratory pressure." These effects were minimized in this model at respiratory rates >/=5.7 and 相似文献   

An excitatory amino acid(s) in the ventrolateral medulla is (are) required for breathing to occur in the anesthetized cat.

The purpose of the present study was to identify sites(s) in the ventrolateral medulla where excitatory amino acids are involved in respiratory control. For this purpose, the respiratory effects produced by bilateral microinjection of excitatory amino acid antagonist drugs were examined while tidal volume (Vt), respiratory rate (f), arterial blood pressure and heart rate were monitored in chloralose-anesthetized cats. Microinjection of kynurenic acid (12.5 nmol) into a site approximately 3 mm rostral to obex, 4 mm lateral to midline and 1.5 mm below the ventral surface produced a decrease in Vt (-20 +/- 2 ml), an increase in f (+20 +/- 3 breaths/min) and a decrease in respiratory minute volume (-108 +/- 19 ml/min) (n = 8). These changes progressed to apnea in each animal tested. No significant changes in blood pressure or heart rate were observed. To determine the excitatory amino acid receptor subtype(s) involved, antagonists of n-methyl-D-aspartate (NMDA) (3-[(RS)-carboxypiperazin-4-yl]-propyl-1-phosphoric acid (CPP] and non-NMDA [6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] receptors were microinjected bilaterally into this site. In the case of CPP, three doses were studied (0.25 nmol, n = 4; 0.75 nmol, n = 3; 2.25 nmol, n = 2). All three doses produced similar decreases in Vt (-12 +/- 1, P less than .05; -10 +/- 1, P less than .05; and -16 +/- 5 ml, respectively) and increases in f (+14 +/- 2, P less than .05; +10 +/- 3, P less than .05; and +12 +/- 3 breaths/min, respectively). None of these animals exhibited apnea.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of decreasing peak flow rate on stomach inflation during bag-valve-mask ventilation

Reducing inspiratory flow rate and peak airway pressure may be important in order to minimise the risk of stomach inflation when ventilating an unprotected airway with positive pressure ventilation. This study was designed to yield enough power to determine whether employing an inspiratory gas flow limiting bag-valve device (SMART BAG, O-Two Medical Technologies Inc., Ontario, Canada) would also decrease the likelihood of stomach inflation in an established bench model of a simulated unintubated respiratory arrest patient. The bench model consists of a training lung (lung compliance, 50 ml/cm H2O; airway resistance, 4 cm H2O/l/s) and a valve simulating lower oesophageal sphincter opening at a pressure of 19 cm H(2)O. One hundred and ninety-one emergency medicine physicians were requested to ventilate the manikin utilising a standard single-person technique for 1 min (respiratory rate, 12/min; Vt, 500 ml) with both a standard adult bag-valve-mask and the SMART BAG. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The SMART BAG versus standard bag-valve-mask resulted in significantly (P < 0.001) lower (mean +/- S.D.) mean airway pressure (14 +/- 2 cm H2O versus 16 +/- 3 cm H2O), respiratory rates (13 +/- 3 breaths per min versus 14 +/- 4 breaths per min), incidence of stomach inflation (4.2% versus 38.7%) and median stomach inflation volumes (351 [range, 18-1211 ml] versus 1426 [20-5882 ml]); lung tidal volumes (538 +/- 97 ml versus 533 +/- 97 ml) were comparable. Inspiratory to expiratory ratios were significantly (P < 0.001) increased (1.7 +/- 0.5 versus 1.5 +/- 0.6). In conclusion, the SMART BAG reduced inspiratory flow, mean airway pressure and both the incidence and actual volume of stomach inflation compared with a standard bag-valve-mask device while maintaining delivered lung tidal volumes and increasing the inspiratory to expiratory ratio.     

Changes in transcutaneous carbon dioxide, oxygen saturation, and respiratory rate after interscalene block

BACKGROUND: We used transcutaneous (TC) carbon dioxide (CO2) monitoring to prospectively evaluate changes in respiratory status after interscalene anesthesia in 45 adults (40 successful and 5 unsuccessful blocks). METHODS: TC-CO2 oxygen saturation and respiratory rate were recorded every minute for 5 minutes before block and every 2 minutes for a total of 30 minutes (15 data sets) after injection of the local anesthetic solution. RESULTS: After successful block, TC-CO2 increased from 41 +/- 5 mm Hg to a maximum value of 44 +/- 6 mm Hg (P < 0.0001) and the respiratory rate increased from 14 +/- 2 breaths/min to a maximum of 20 +/- 4 breaths/min (P < 0.001). The increase in TC-CO2 was > or = 5 mm Hg in 11 patients and > or = 10 mm Hg in 4 patients, with a maximum increase of 12 mm Hg. Of the 600 TC-CO2 data points recorded (15 each from the 40 patients with a successful block), 62 (10.3%) showed a TC-CO2 value of 50 mm Hg or greater, with a maximum value of 57 mm Hg. No significant change in TC-CO2 or respiratory rate was seen in the five patients with unsuccessful block. CONCLUSION: After interscalene blockade, we found an increase in respiratory rate and hypercarbia that resulted in no clinically significant effect.