Maximal values of sniff nasal inspiratory pressure in healthy subjects.

BACKGROUND--Inspiratory muscle strength is often better reflected by oesophageal pressure during a maximal sniff (sniff POES) than by maximal inspiratory pressure (PImax). Sniff POES can be estimated non-invasively by measuring the sniff nasal inspiratory pressure (SNIP). The aim was to establish maximal normal values for the SNIP and to compare them with PImax. METHODS--One hundred and sixty healthy subjects (80 men) aged 20-80 years were recruited. All subjects had a forced vital capacity (FVC) of > 80%, a forced expiratory volume in one second (FEV1)/FVC of > 85% predicted value, and a body mass index of 18-31 kg/m2. Because PImax is known to be reduced in the supine posture, the SNIP was measured in both the sitting and the supine positions. PImax sustained over one second was measured from functional residual capacity (FRC) in the sitting position with a standard flanged mouthpiece during four manoeuvres. SNIP was measured from FRC in the sitting and supine positions using a catheter through a plug occluding one nostril during 10 maximal sniffs through the contralateral nostril. For each test the largest pressure measured in cm H2O was taken into account. RESULTS--For both men and women maximal SNIP was negatively correlated with age, and was similar in the sitting and the supine positions. In the sitting position maximal SNIP was greater or equal to PImax in 107 of 160 subjects. The mean (SD) ratio SNIP/PImax was 1.08 (0.22) in men and 1.17 (0.29) in women. CONCLUSIONS--Normal values of maximal SNIP can be predicted from age and sex. Maximal SNIP is similar in the sitting and the supine position and is significantly higher than PImax in healthy subjects. The low level of agreement between maximal SNIP and PImax indicates that the two manoeuvres are not interchangeable but complementary.     

Respiratory function and ribcage contribution to ventilation in body positions commonly used during anesthesia

Lung function tests are normally performed in the upright position, whereas anesthesia is usually administered with the patient in the supine position, and occasionally in other postures. We therefore compared forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), functional residual capacity (FRC), and ribcage contribution to ventilation by respiratory inductive plethysmography in 13 conscious healthy male volunteers, sitting and in four horizontal positions used during anesthesia. Forced vital capacity and FEV1 were similar in all positions, except for a significant mean increase in FVC of 300 mL (SD 213) when sitting compared with when supine (P less than 0.001). The mean decrease in FRC was 806 mL (SD 293) between the sitting and supine positions (P less than 0.001). A significant increase in FRC occurred (252 mL, SD 329, P less than 0.01) when supine subjects raised their arms above their heads as required for computed tomography. Functional residual capacity in the prone and lateral positions was significantly larger than in the supine position (mean change 350 mL, P less than 0.001), but was still some 450 mL less than in the sitting position. Mean ribcage contribution was similar in all horizontal positions (32%-36%), whereas supine values were significantly different from those of the sitting position (mean 70%, SD 11, P less than 0.001). In conclusion, the various horizontal postures studied have no effect on FVC, FEV1, or ribcage contribution to ventilation. However, FRC in the prone, lateral, and arms-up positions is on average 250 mL larger than in the supine position, an observation that may affect gas exchange during anesthesia in these positions.     

Relation between nocturnal symptoms and changes in lung function on lying down in asthmatic children.

Nocturnal symptoms are common in young asthmatic children. Such symptoms may be caused by increased impairment of lung function when they adopt the supine posture. Thirty one children aged 2.8-8.3 years were studied, of whom 20 had asthma (10 with frequent nocturnal symptoms) and 11 had no respiratory problems (control subjects). Peak expiratory flow (PEF) was measured with a Wright's peak flow meter and functional residual capacity (FRC) by a helium gas dilution technique after 30 minutes of lying supine; the values were compared with FRC measured sitting and PEF standing. Peak flow fell significantly on adoption of the supine posture in the asthmatic children, but there was no difference in this fall between the asthmatic children with and without nocturnal symptoms. FRC also fell on adoption of the supine posture, but the decrease in FRC was significant only in the control children and the asthmatic children without nocturnal symptoms. The failure to find a greater fall in PEF or a greater change in FRC on adoption of the supine posture among asthmatic children with nocturnal symptoms suggests that mechanisms other than increased impairment of lung function are responsible for nocturnal asthma.     

Factors Affecting Lung Function: A Review of the Literature

Lung function reference values are traditionally based on anthropometric factors, such as weight, height, sex, and age. FVC and FEV₁ decline with age, while volumes and capacities, such as RV and FRC, increase. TLC, VC, RV, FVC and FEV₁ are affected by height, since they are proportional to body size. This means that a tall individual will experience greater decrease in lung volumes as they get older. Some variables, such as FRC and ERV, decline exponentially with an increase in weight, to the extent that tidal volume in morbidly obese patients can be close to that of RV. Men have longer airways than women, causing greater specific resistance in the respiratory tract. The increased work of breathing to increase ventilation among women means that their consumption of oxygen is higher than men under similar conditions of physical intensity. Lung volumes are higher when the subject is standing than in other positions. DLCO is significantly higher in supine positions than in sitting or standing positions, but the difference between sitting and standing positions is not significant. Anthropometric characteristics are insufficient to explain differences in lung function between different ethnic groups, underlining the importance of considering other factors in addition to the conventional anthropometric measurements.     

In vivo assessment of diaphragm contraction by ultrasound in normal subjects.

BACKGROUND--Ultrasound allows observation of the thickness of the diaphragm in the zone of apposition in vivo during relaxation and maximum inspiratory efforts. METHODS--Changes of diaphragm thickness were studied by B mode (two dimensional) ultrasound in 13 healthy men aged 29-54 years in the seated position. A high resolution 7.5 MHz ultrasound transducer was held perpendicular to the chest wall in the line of a right intercostal space between the anteroaxillary and mid-axillary lines to observe the diaphragm in the zone of apposition 0.5-2 cm below the costophrenic angle. The changes of thickness were observed while breath holding at total lung capacity (TLC), functional residual capacity (FRC), and residual volume (RV). At FRC the thickness while relaxing against a closed mouthpiece and during a maximum inspiratory mouth pressure (PImax) manoeuvre was recorded. The thickening ratio (TR) was calculated as TR = thickness during PImax manoeuvre/thickness while relaxing. RESULTS--Mean (SD) thickness was 4.5 (0.9) mm at TLC, 1.7 (0.2) mm at FRC, and 1.6 (0.2) mm at RV. During the PImax manoeuvre at FRC mean thickness increased from 1.7 (0.2) mm during relaxation to 4.4 (1.4) mm, while mean PImax and TR were -104 (33) cm H2O and 2.6 (0.7), respectively. There was a high degree of correlation between TR and the pressure achieved during the maximum inspiratory manoeuvre (r = -0.82). CONCLUSIONS--Ultrasound provides a non-invasive assessment of diaphragm thickness with change of lung volume and during the PImax manoeuvre which should prove useful in assessing diaphragm mass and contraction in respiratory and muscle disease.     

Effects of barbiturate anesthesia on functional residual capacity and ribcage/diaphragm contributions to ventilation

The effect of iv methohexital infusion anesthesia on functional residual capacity (FRC) (helium dilution) in 14 surgical patients (age 23 to 59 years) was determined. Eight subjects were studied wearing an inflatable mask, sealed with surgical lubricant. They showed a mean +/- SD 3.5 +/- 6.4% FRC decrease (no significance). Six subjects studied via mouthpiece awake and via endotracheal tube during anesthesia showed a mean 22 +/- 19% reduction in FRC, significantly greater than face mask studies (P less than 0.05). The greatest FRC decrease occurred in subjects with repetitive or protracted coughing after intubation. The serum methohexital level was 6.6 +/- 3.6 micrograms/ml for intubated patients, and 6.0 +/- 1.1 micrograms/ml in those with face mask (no significance). The depth of anesthesia was sufficient to produce a 50% reduction in ventilatory response to CO2 rebreathing, from 15.8 to 8.7 l/min/% CO2. Respitrace plethysmography indicated a 38 +/- 12% ribcage contribution to tidal volume during quiet breathing, which increased to 47 +/- 14% with CO2 breathing (end-tidal FCO2 9-10%). There was no dimunition of ribcage contribution during anesthesia in either group, irrespective of CO2 concentration. The authors interpret their findings to indicate that iv methohexital anesthesia does not produce FRC reduction, in contrast to an inhaled anesthetic such as halothane. It is proposed that this difference may be related to maintenance of coordinated ribcage/diaphragm muscle activity, because ribcage activity is markedly suppressed by halothane. In addition, it is proposed that FRC reduction in intubated subjects was the result of a confounding variable, namely coughing in response to the endotracheal tube.     

Effects of posture on carbon dioxide responsiveness in patients with obstructive sleep apnoea.

BACKGROUND--It is well known that upper airway resistance increases with postural change from a sitting to supine position in patients with obstructive sleep apnoea (OSA). It is not known, however, how the postural change affects the ventilatory and occlusion pressure response to hypercapnia in patients with OSA when awake. METHODS--The responses of minute ventilation (VE) and mouth pressure 0.1 seconds after the onset of occluded inspiration (P0.1) to progressive hypercapnia (delta VE/delta PCO2, delta P0.1/delta PCO2) both in sitting and supine positions were measured in 20 patients with OSA. The ratio of the two (delta VE/delta P0.1) was obtained as an index of breathing efficiency. The postural changes in response to carbon dioxide (CO2) after uvulopalatopharyngoplasty (UPPP) were also compared in seven patients with OSA. RESULTS--There were no significant changes in the resting values of end tidal PCO2, P0.1, or VE between the two positions. During CO2 rebreathing, delta VE/delta PCO2 did not differ between the two positions, but delta P0.1/delta PCO2 was significantly higher in the supine than in the sitting position (supine, mean 0.67 (SE 0.09) cm H2O/mm Hg; sitting, mean 0.57 (SE 0.08) cm H2O/mm Hg), and delta VE/delta P0.1 decreased significantly from the sitting to the supine position (sitting, 4.6 (0.4) l/min/cm H2O; supine, 3.9 (0.4) l/min/cm H2O). In seven patients with OSA who underwent UPPP, delta VE/delta P0.1 improved significantly in the supine position and postural change in delta VE/delta P0.1 was eliminated. CONCLUSIONS--These results suggest that in patients with OSA the inspiratory drive in the supine position increases to maintain the same level of ventilation as in the sitting position, and that the postural change from sitting to supine reduces breathing efficiency. Load compensation mechanisms of patients with OSA appear to be intact while awake in response to the rise in upper airway resistance.     

The diaphragmatic compound muscle action potentials (DCMAPs) at different lung volumes--a prospective electrophysiological study of the respiratory system

Phrenic nerve conduction study and measurements of static lung volumes such as functional residual capacity (FRC), total lung capacity (TLC) and residual volumes (RV) using body plethysmography were carried out in 31 normal healthy male subjects (31 +/- 8 years). The objective was to correlate changes in latency, amplitude, duration and area of diaphragmatic compound muscle action potential (DCMAPs) with lung volumes and changes in them with changes in postures. The mean phrenic nerve latency did not show any significant change with lung volumes or postures, but the latency and height of the subject had a significant correlationship (r = 0.68). The peak to peak amplitude of DCMAP showed a significant relationship with the quantitative lung volumes (r = 0.65). The amplitude was significantly higher and duration reduced (p < 0.001) at TLC as compared with those at measured FRC and RV in both sitting and supine postures. The area under the curve did not change significantly. Similarly, amplitudes and latency did not show any significant relation with other anthropometric parameters. The study evaluates a new quantitative relationship between DCMAPs amplitude and lung volumes. This may be carefully used along with other clinical parameters in critically ill patients for an early weaning from ventilator. Posture exerts minimal influence on DCMAPs amplitude; since DCMAPs amplitudes depends on the position of the diaphragm which in turn depends on dipolic potential, its electromagnetic fields and its moving angle subtends at the recording electrode, one can confidently use it to predict lung volume in respiratory failure due to neuromuscular diseases where subjective lung function assessment is impossible. However, a further study is in process in the critical care unit to confirm its utility.     

PERIOPERATIVE CHANGES IN FUNCTIONAL RESIDUAL CAPACITY IN MORBIDLY OBESE PATIENTS

Functional residual capacity (FRC) was measured before and afterinduction of anaesthesia for jejunoileal bypass surgery in 30morbidly obese patients. The onset of anaesthesia was associatedwith a 51% reduction in FRC from 2.2 litre to 1.0 litre. Eighteenof the patients were investigated more extensively; in thesesubjects FRC was reduced below the control values of residualvolume (RV) with the onset of anaesthesia, but recovered towardsbaseline after laparotomy incision. Reduction in FRC is relatedto baseline vital capacity (VC) and FRC and is much greaterthan that reported for patients of normal weight.     

DETECTION AND REVERSAL OF PULMONARY ABSORPTION COLLAPSE

Six healthy seated male subjects (aged 36–54 yr) inhaled100% oxygen for 10 min at normal lung volume and then for afurther 5 min with forced maximal expirations. Following thismanoeuvre, changes in arterial Po₂ ranged from a decrease of16.7 kPa to an increase of 2 kPa (—125 to +15 mm Hg) whilebreathing 100% oxygen, and a decrease of 1.8 kPa to an increaseof 1.1 kPa (—13.5 to + 8.6 mm Hg) while breathing air.Functional residual capacity (FRC) was unchanged in one subject,but decreased by 0.04–1.15 litre in the others. The chestradiograph was unaltered in the subjects with zero and 0.04litre decreases in FRC. Three of the other subjects showed lineshadows at the bases, while the subject with the largest decreasein FRC showed extensive areas of collapse. There was a goodcorrelation between changes in arterial Po₂, FRC and the chestradiograph. Substernal discomfort was felt when those subjectswith positive radiographic changes attempted to make a maximalinspiration. All changes were reversed by taking five maximalforced inspirations. Arterial Po₂ changes while breathing 100%oxygen provided the most sensitive indication of collapse. Changesin FRC and arterial Po2 while breathing air were generally withinthe normal reference range of these variables, and thereforeof little diagnostic value in the absence of control measurements.Under such circumstances, chest radiography seems to be themost sensitive indication of pulmonary collapse occurring inthe upright position. ^* Present address: Great Yarmouth General Hospital, Dene Side,Great Yarmouth NR30 2LX.     

Pulmonary contusion causes long-term respiratory dysfunction with decreased functional residual capacity

To elucidate the mechanism of persistent dyspnea after blunt chest trauma, we prospectively studied the pulmonary function of 18 patients with blunt chest trauma for 6 months. Nine of the patients had flail chest and 12 had pulmonary contusion (PC). Pulmonary function was evaluated using spirometry, arterial blood gas analysis, chest x-ray studies and CT scans. Functional residual capacity (FRC) remained significantly reduced throughout the 6 months in patients with PC. Such patients experienced a fall in Pao2 when changed from a sitting position to a supine position and they had fibrous changes in the contused lung as demonstrated by CT scans at 6 months after injury. These findings were supported in an additional study of another 20 patients who had suffered PC 1 to 4 years previously. This study demonstrated that pulmonary function recovered within 6 months in patients without PC even with a residual deformity of the thoracic wall caused by flail chest, while patients with PC had decreased FRC and a fall in Pao2 when moved to the supine position even several years after injury. This might be related to the persistent dyspnea seen after blunt chest trauma.     

Effect of posture on lung volume: airway closure and gas exchange in hemidiaphragmatic paralysis.

The effects of posture on lung volume, airway closure, and gas exchange were studied in eight patients with hemidiaphragmatic paralysis. The mean vital capacity in the sitting position was 81% of predicted normal, and in the supine posture fell by a further 19% in right-sided but only 10% in left-sided paralysis. The mean arterial oxygen tension was less than predicted in the sitting posture and fell significantly on lying. Single breath gas transfer factor was normal in all cases whereas the diffusion coefficient was greater than predicted in the sitting posture and rose even further on lying. Closing volume showed no positional change but closing volume as a percentage of vital capacity was higher in the supine position. Regional airways closure was expressed as the relationship expiratory reserve volume minus closing volume. Negative values were found in only two of the subjects in the sitting position but seven had negative values supine, indicating significant airway closure during tidal breathing in this position.     

Postural changes in respiratory function

Changes in body position alters the functional residual capacity (FRC). Most anesthetics reduce FRC in the recumbent but not sitting position. Inspired gas distribution in anesthesia-paralyzed subjects whose lungs are mechanically ventilated, is different from that in the awake state in all but the prone position. The function of the diaphragm is altered by postural changes. The pattern of motion of the diaphragm is different during mechanical ventilation than during spontaneous breathing. Also the end-expiratory shape is affected by induction of anesthesia, but this shape change contributes little to the reduction of FRC. The distribution of pulmonary blood flow is determined not only by gravity, but also by an intrinsic non-gravity dependent factor. These two factors can be additive in some positions but opposing in others.     

Impact of caudal block on functional residual capacity and ventilation distribution in anaesthetized preschool children

Introduction: In children, general anaesthesia is often performed in combination with regional anaesthesia and caudal block (CB) is probably the most commonly used central neuroaxial blockade. The administration of local anaesthetics results in a motor blockade. The impact of this motor blockade induced by CB on the functional residual capacity (FRC) and ventilation distribution is unknown. The aim of this study was to determine the impact of CB versus control on FRC and ventilation distribution in preschool children. We hypothesized that an effective CB would lead to an increase of FRC and ventilation distribution while these parameters would remain unchanged in the control group. Methods: After approval from the local Ethics Committee, 52 preschool children (15–30 kg, 3–8 years) without cardiopulmonary disease who were to undergo elective surgery requiring combined general/regional anesthesia with a CB, were randomly allocated into two groups: CB (n = 26) or control (n = 26). Anesthesia was standardized using a propofol TCI for children. All children were breathing spontaneously via a laryngeal mask airway. FRC and lung clearance index (LCI), a measure of ventilation distribution, were calculated using a sulfur‐hexafluoride gas (SF₆) multibreath washout technique. A blinded reviewer performed off‐line analyses of the data. Following the first measurement in the supine position (baseline), all children were turned into the left‐lateral position. The CB group received a CB (0.2 ml·kg^‐1 bupivacaine 0.25% + epinephrine 1: 200 000 test dose and 0.8 ml·kg^‐1 bupivacaine 0.175%), while in the control group no intervention took place. After 5 min in the lateral position, all children were turned back to the supine position. After 15 min, the effectiveness of the CB was tested by pinching the skin at the L1 level with any movement being taken as a noneffective block (n = 0), and the second FRC assessment was performed in both groups. Results: At baseline, FRC and LCI were similar for the two groups. In the CB group, FRC (mean ± SD) increased from 17.0 ± 4.3 ml·kg^‐1 to 20.5 ± 5.1 ml·kg^‐1 (P < 0.0001) after an effective CB while FRC in the control group remained unchanged (17.2 ± 4.9 ml·kg^‐1 to 17.1 ± 4.8 ml·kg^‐1 (P = 0.0757). At the same time, the LCI decreased from 12.0 ± 2.5 to 9.37 ± 1.7 (P < 0.0001) in the CB group, while it remained constant in the control group (10.8 ± 2.7 vs 10.7 ± 2.6, P = 0.1515). Conclusions: CB resulted in a significantly increased FRC and ventilation distribution, whereas these parameters did not change in the control group. This indicates that a CB could have a major impact on respiratory function in anaesthetized, spontaneously breathing children. Additionally, the constant values for FRC and LCI in the control group showed that there was no ‘over‐time’ effect on these two parameters during the assessed study period. Acknowledgement: The study was funded by the Department of Anaesthesia, University of Basel, Switzerland and by the Swiss Association of Anaesthesia and Reanimation (SGAR).     

EFFECT ON LUNG VOLUMES OF OXYGEN CONCENTRATION WHEN BREATHING IS RESTRICTED

We have examined the effect of the fractional concentrationof nitrogen (FlN2) on the decrease in lung volumes which occursduring restricted breathing with oxygen-nitrogen mixtures. Conscioushuman subjects breathed one of five gas mixtures of oxygen andnitrogen for 15 min on each of five occasions. For the final5 min of each 15-min period, functional residual capacity (FRC)was reduced by one tidal volume, by external pressur-ization.After return to normal breathing, the subjects showed a statisticallysignificant decrease in FRC and residual volume (RV), whichbecame larger as F/o increased from 30% to 100%. This reductionin lung volumes was resistant to early re-expansion. The maximumdecrease in both FRC and RV was found with 100% oxygen, andwas 10% of the control lung volumes. The use of a mixture of75 % nitrogen and 25 % oxygen prevented this decrease in lungvolumes. Nitrogen 50% reduced the decrease in FRC, but did notaffect the decrease in RV. The difference in effect on lungvolumes between Fl02 25% and 30% was statistically significant,indicating a watershed area for Fl between 70% and 75%. (Br.J. Anaesth. 1993; 70: 259–266)     

The effect of thoracic epidural analgesia on respiratory function after cholecystectomy

To assess the effect of thoracic epidural analgesia (TEA) on postoperative respiratory function and pulmonary complications, a prospective randomized trial was conducted in patients undergoing cholecystectomy. One hundred patients were allocated to TEA (n = 30), TEA + general anesthesia (TEA + GA) (n = 30), or general anaesthesia (GA) (n = 40) groups. Respiratory function was analysed by measuring forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), functional residual capacity (FRC), total lung capacity (TLC), peak expiratory flow (PEF) in the supine and sitting postures, and arterial blood gases. Postoperative pulmonary complications were carefully documented. TEA significantly prevented the postoperative deterioration of respiratory function as compared with general anaesthesia. FVC, FEV1 and PEF decreased by 20% in patients receiving TEA, in contrast to 55% in patients after GA on the day of operation. This improvement continued until the 2nd day after operation, when FVC, FEV1 and PEF and their recovery rates were equal in all groups. In the sitting posture the preoperative FVC, FEV1 and PEF were about 10% greater than in the supine position. After operation, this difference was further increased. The preoperative difference of 27% in FRC between the sitting and supine postures was maintained after operation. PaO2 decreased by 0.8 kPa after TEA, by 1.5 kPa after TEA + GA with the lowest value on the 2nd postoperative day and by 1.5 kPa after GA, with the lowest value immediately after operation. Simultaneous hypercarbia indicated hypoventilation, which may have contributed to impaired respiratory function on the following days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lung mechanics after cardiac valve replacement.

Fourteen patients undergoing single aortic or mitral valve replacement had measurements made of lung volumes, static pressure-volume (P-V) relationships, and conductance-pressure relationships during deflation before operation and again between one and two years later. At follow-up, total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), and static tidal compliance (slope of static P-V deflation line for one litre above FRC) had increased significantly, in association with a decrease in heart size. There was a change in the shape and position of some P-V curves both in the aortic and mitral patients. In the patients with aortic disease P-V deflation curves shifted to the left after operation. In the patients with mitral disease the P-V deflation curves before operation crossed those measured after operation, so that at high lung volumes recoil became less after operation, but at low lung volumes recoil increased. Conductance had increased at high lung volumes. The data suggest that in longstanding pulmonary congestion, airways are more rigid making them less distensible at high and less compressible at low transpulmonary pressures than after operation when congestion has been at least partly relieved.     

The influence of position on ventilation-perfusion distribution after abdominal surgery

The effects of a change in position on gas exchange and ventilation perfusion (VA/Q) distribution were studied in 12 patients, after abdominal surgery. VA/Q distribution was determined from retention and excretion curves of six inert gases of different solubilities, in supine and sitting patients, during spontaneous breathing. Changing position from supine to sitting resulted in an increase in minute ventilation and a decrease in PaCO2 without any change in PaO2. With regard to VA/Q distribution, an estimated shunt of 5.2% +/- 3.4 was documented in all the patients in the supine position, and was associated with a large percentage of low VA/Q regions (20.0% +/- 13.0) in six of them. Patients with associated estimated shunt and low VA/Q regions were those with the greatest amount of venous admixture (respectively: 27.3% +/- 7.2, and 14.9% +/- 3.0, for patients without low VA/Q regions, P less than 0.01). When patients were placed in the sitting position, the estimated shunt was not reduced, but the percentage of low VA/Q regions decreased when it was documented. Despite the improvement of VA/Q distribution in the sitting position, the lack of significant change in PaO2 may be explained by the simultaneous decrease in PVO2 caused by a decrease in cardiac output.     

A comparative analysis of transcutaneous oximetry (tcPO2) during oxygen inhalation and leg dependency in severe peripheral arterial occlusive disease.

Transcutaneous oximetry (tcPO2) performed during either oxygen inhalation or leg dependency was intra-individually compared in 64 patients suffering from a peripheral arterial occlusive disease, with and without critical limb ischemia. Among the 81 extremities investigated, 29 had a moderate peripheral arterial occlusive disease (6 in stage I, 23 in stage II) and 52 were initially affected by rest pain or ulceration (stage III/IV). Thirty-seven legs out of the latter improved under conservative treatment. In the remaining 15 limbs, vascular surgery or an amputation became necessary. The tcPO2 was measured at the forefoot with the patient in supine and sitting positions while breathing room air and in the supine position while inhaling 100% oxygen. In limbs with a tcPO2 below 15 mm Hg of patients in the supine position breathing room air, leg dependency generally provoked larger tcPO2 increases than oxygen inhalation. This difference between oxygen inhalation while supine and room air breathing leg dependency tcPO2 values exhibited an approximately linear correlation with the resting tcPO2. Responses of tcPO2 to leg dependency and oxygen inhalation seemed to reflect different mechanisms, that is, microvascular flow redistribution and supine perfusion reserve, respectively. The best discrimination of critical limb ischemia was observed for the tcPO2 of patients breathing room air while in the supine position, which was not surpassed by either the oxygen inhalation or the leg dependency test. Satisfactory results were achieved by combining limits for, first, supine (10 mm Hg) and sitting (45 mm Hg) tcPO2, as well as, second, ankle arterial pressure (60 mm Hg) and supine tcPO2 (10 mm Hg).     

Oral airway resistance during wakefulness in patients with obstructive sleep apnoea

BACKGROUND: Patients with obstructive sleep apnoea (OSA) have a number of upper airway structural abnormalities which may influence the resistance of the oral airway to airflow. There have been no systematic studies of the flow dynamics of the oral cavity in such patients. METHODS: Inspiratory oral airway resistance to airflow (RO) was measured in 13 awake patients with OSA in both the upright and supine positions (neck position constant). Each subject breathed via a mouthpiece while the nasal airway was occluded with a nasal mask. RESULTS: In the upright position the mean (SE) RO was 1.26 (0. 19) cm H2O/l/s (at 0.4 l/s) which increased to 2.01 (0.43) cm H2O/l/s when supine (p<0.05, paired t test). The magnitude of this change correlated negatively with the respiratory disturbance index (r = -0.60, p = 0.03). CONCLUSION: In awake patients with OSA RO is normal when upright but abnormally raised when in the supine position.