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PubMed2003

[Determination of an expected plantar pressure threshold: dimensionless approach use to reduce the variability of the plantar pressures].

OBJECTIVE: The aim of this study was to verify that the determination of walking velocities proportional to the leg lengths of the subjects together with the dimensionless expression of the results enable us to decrease the variability and to determine a plantar pressure threshold. MATERIALS AND METHODS: Fifteen male subjects performed two walking tests on a treadmill at imposed velocities (V1 and V3) and similar velocities (V27 and V37). Similar velocities (Vsim =Nfr(g.Li)(0.5)) were determined from two fractions of the Froude number (Nfr), the gravitational acceleration (g) and the length of the lower limb (Li) of the subjects. An in-shoe plantar pressure measurement system allowed the pressure peaks to be recorded. The peak of pressure (p) was reported to the step length (a) and the weight of the subject (mg) for the dimensionless pressure peaks (Dim(P)=p.a2/mg) to be expressed. The coefficients of variability (CoV) and extends of the dimensionless pressure peaks (Epp) have been studied at the different imposed walking velocities. RESULTS: The CoV and Epp of the dimensionless pressure peaks recorded at V27 and V37 (similar velocities) are from 2 to 9% and 3 to 22% lower than those observed at V1 and V3, respectively. DISCUSSION-CONCLUSION: The analysis of the pressure peaks CoV and Epp shows that the method should allow a data bank usable to detect the effects of a disability on the plantar pressures to be elaborated. Indeed, our results enable us to define a plantar pressure pattern with a variability lower than those reported in most scientific articles.

Adult↗

PubMed2005

The relationship between blood pressure, pulse pressure and right ventricular function following an atrial switch procedure for complete transposition of the great arteries.

BACKGROUND: The pressure overload may be responsible for the failure of the systemic ventricle. No study so far has evaluated the association between arterial blood pressure values and right ventricular function in adults with atrially corrected complete transposition. METHODS: This was a retrospective analysis. The studied population consisted of 60 patients with complete transposition, 11.5+/-2.7 years after atrial switch procedure, divided into subgroups according to the severity of systemic ventricular dysfunction (right ventricular ejection fraction < or = 0.40 vs. > 0.40), and the severity of perfusion abnormalities in the radionuclide study (absent or mild vs. moderate-to-severe). RESULTS: All patients had blood pressure values (systolic 109.1+/-11.7 mm Hg and diastolic 72.3+/-9.7 mm Hg) within the normal range. Systolic blood pressure values correlated inversely with right ventricular ejection fraction (r = -0.450; p < 0.001). Compared to patients with systolic blood pressure below median values, patients with "elevated" blood pressure had lower right ventricular ejection fraction (32.6+/-6.3 vs. 38.9.+/-7.2; p < or = 0.002) and more significant perfusion abnormalities (1.5+/-1.0 vs. 2.9+/-1.5; p < or = 0.001). In a multivariate backward logistic regression model age at surgery and at the time of the study, systolic blood pressure at rest predicted impaired right ventricular ejection fraction (p < 0.02). Greater pulse pressure at peak exercise female sex were associated with greater more severe perfusion abnormalities (p < 0.01). CONCLUSIONS: There is a significant correlation between blood pressure values and indices of right ventricular dysfunction in patients who underwent an atrial switch procedure for complete transposition. Blood pressure values might be considered as a surrogate end point in these patients.

Adolescent↗

PubMed2006

A dose-response curve for the negative bias pressure of an intrathoracic pressure regulator during CPR.

An intrathoracic pressure regulator (ITPR) is a device that can be added to the external end of a tracheal tube to create controlled negative airway pressure between positive pressure ventilations. The resulting downward bias of the airway pressure baseline promotes increased venous return and enhanced circulation during CPR and also during hypovolemic shock. In the present study, we exercised a mathematical model of the human cardiopulmonary system, including airways, lungs, a four chambered heart, great vessels, peripheral vascular beds, and the biomechanics of chest compression and recoil, to determine the relationship between systemic perfusion pressure during CPR and the value of baseline negative airway pressure in an ITPR. Perfusion pressure increases approximately 50% as baseline airway pressure falls from zero to -10 cm H2O. Thereafter perfusion pressure plateaus. Negative bias pressures exceeding -10 cm H2O are not needed in ITPR-CPR.

Blood Circulation↗

PubMed1996

Does intrabiliary pressure predict basal sphincter of Oddi pressure? A study in patients with and without gallbladders.

BACKGROUND: The endoscopic measurement of sphincter of Oddi pressure is a technically difficult procedure requiring significant expertise. Intrabiliary pressure is technically easy to measure. Furthermore, since it is believed that the pathogenesis of pain in patients with sphincter of Oddi dysfunction is attributable to increased intrabiliary pressure, its measurement may be more clinically relevant than measurement of sphincter of Oddi pressure. METHODS: Intrabiliary pressures were blindly measured in 54 patients who had sphincter of Oddi manometry for abdominal pain. RESULTS: In all patients intrabiliary pressure was significantly higher in patients with sphincter of Oddi dysfunction than those with normal sphincter of Oddi pressure (19.6 +/- 2.2 vs 9.6 +/- 1.2 mm Hg; p < 0.01). These findings were similar when patients were stratified according to presence of intact gallbladder (19.3 +/- 1.6 vs 8.8 +/- 1.4; p < 0.01) and to patients without a gallbladder (20.1 +/- 3.8 vs 12/1 +/- 1.3; p = .034). There was positive correlation between intrabiliary pressure and sphincter of Oddi basal pressure. This correlation was significant both in patients with and without gallbladders. CONCLUSIONS: These data suggest that increased intrabiliary pressure may be a useful surrogate marker of sphincter of Oddi dysfunction.

Abdominal Pain↗

PubMed1979

Variations in inspiratory:expiratory ratio and airway pressure wave form during mechanical ventilation: the significance of mean airway pressure.

Twelve neonates with severe lung disease were studied while mechanically ventilated with volume pre-set infant ventilators, using different I:E ratios and different airway pressure waves. While FIO2 tidal volume, respiratory rate, and PEEP remained constant, I:E ratios were increased, first by reducing inspiratory flow rate, which produced a triangular pressure wave, and then by using an inspiratory time hold mechanism, which produced an inspiratory plateau or squared pressure wave. Peak inspiratory pressure, mean airway pressure, PaO2, PaCO2, pH, and blood pressure were measured and compared for each I:E ratio and pressure wave combination. In all patients, increases in oxygenation appeared to be directly related to increases in MAP. Optimum oxygenation and ventilation occurred with the I:E ratio and pressure wave combination that produced the highest MAP. Because MAP changes with any alteration in PEEP, I:E ratio, or airway pressure wave, it is a clinically useful composite measure of all pressures transmitted to the airways by a mechanical ventilator.

Humans↗

PubMed2003

Is systolic blood pressure sufficient for classification of blood pressure and determination of hypertension based on JNC-VI in an Iranian adult population? Tehran lipid and glucose study (TLGS).

The purpose of this study was to determine if systolic blood pressure (SBP) by itself is sufficient for the JNC-VI (Sixth Report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure)-based classification of blood pressure of Tehranian adult population. Clinically, SBP and diastolic blood pressure (DBP) are sometimes at different stages in the same individual and the higher stage is considered to classify blood pressure level. The prevalence of disparate levels of SBP and DBP has only recently been noticed. Some researches have reported the importance of SBP level, and not DBP, in determining the appropriate classification of hypertension even in those undergoing treatment. Data were collected for 3823 men and 5159 women aged 20-69 years who were not using antihypertensive medication, in the Tehran Lipid and Glucose Study (TLGS), a cross-sectional phase of a large epidemiological study first established in 1999. The study used the mean of two separate blood pressure measurements in each individual. High blood pressure is defined according to the highest level of SBP or DBP. In 86.3% of the subjects, blood pressure stage was determined according to SBP and in 90.0% of them according to DBP. In 77.4% of the subjects (75.7% of men and 78.7% of women), SBP determined blood pressure in the same stage as DBP did. The role of SBP was the most prominent in age groups 20-29 and 60-69 years (91.4 and 90.8%, respectively) and the least in age group 40-49 years (80.4% of the subjects). DBP had a more prominent role in younger ages and the least significance in older ages. In conclusion, SBP has a more prominent role than DBP in determining blood pressure stage according to JNC-VI only in the 60-69-year-old group. The role of DBP is more prominent in other age groups.

Adult↗

PubMed1980

Blood pressure variability in man: its relation to high blood pressure, age and baroreflex sensitivity.

1. Intra-arterial blood pressure and heart rate were recorded for 24 h in ambulant hospitalized patients of variable age who had normal blood pressure or essential hypertension. Mean 24 h values, standard deviations and variation coefficient were obtained as the averages of values separately analysed for 48 consecutive half-hour periods. 2. In older subjects standard deviation and variation coefficient for mean arterial pressure were greater than in younger subjects with similar pressure values, whereas standard deviation and variation coefficient for mean arterial pressure were greater than in younger subjects with similar pressure values, whereas standard deviation aations and variation coefficient were obtained as the averages of values separately analysed for 48 consecurive half-hour periods. 2. In older subjects standard deviation and variation coefficient for mean arterial pressure were greater than in younger subjects with similar pressure values, whereas standard deviation and variation coefficient for heart rate were smaller. 3. In hypertensive subjects standard deviation for mean arterial pressure was greater than in normotensive subjects of similar ages, but this was not the case for variation coefficient, which was slightly smaller in the former than in the latter group. Normotensive and hypertensive subjects showed no difference in standard deviation and variation coefficient for heart rate. 4. In both normotensive and hypertensive subjects standard deviation and even more so variation coefficient were slightly or not related to arterial baroreflex sensitivity as measured by various methods (phenylephrine, neck suction etc.). 5. It is concluded that blood pressure variability increases and heart rate variability decreases with age, but that changes in variability are not so obvious in hypertension. Also, differences in variability among subjects are only marginally explained by differences in baroreflex function.

Adult↗

PubMed1999

Estimation of alveolar pressure during speech using direct measures of tracheal pressure.

The pressure in the alveoli of the lungs, created by the elastic recoil of the lungs and respiratory muscle activity, is referred to as alveolar pressure (Pa). The extent to which tracheal pressure (Pt) approximates Pa depends on the resistance to airflow offered by structures above and below the point at which tracheal pressure is measured. An understanding of the relationship among Pa, Pt, and upper and lower airway resistance, and how these values fluctuate during speech, could aid in interpretation and modeling of speech aerodynamics. The purpose of this study was to (a) obtain values for lower airway resistance (Rlow), (b) use these Rlow values to estimate Pa during speech, and (c) quantify the degree to which Pt approximates Pa during production of voiced and voiceless sounds, in comparison to inhalation. In addition, the results were discussed in terms of the degree to which the respiratory system functions as a pressure source. Tracheal pressure (obtained with tracheal puncture) and airflow were measured during sentence production in 6 subjects. Using a technique introduced in this paper, Rlow was determined from measures of tracheal pressure and flow obtained during a sudden change in upper airway resistance because of release of a voiceless plosive. Mean Rlow values ranged from 0.14 to 0.32 kPa/(l/s). Each subject's mean Rlow was used to derive a time-varying measure of Pa during speech from continuous measures of tracheal pressure and airflow. Pt was approximately 95% of Pa during phonation (i.e., when the vocal folds were adducted), 75% of Pa during release of the voiceless stop consonant /p/, and 55% of Pa during inhalation (i.e., when the vocal folds were abducted). Therefore, the degree to which the respiratory system functioned as an ideal pressure source varied during speech. The ability to estimate Pa provides a measure of the pressure produced by the respiratory system that is not influenced by laryngeal activity.

Adult↗

PubMed1999

Analysis of pressure achieved by various materials used for pressure dressings.

BACKGROUND: To minimize the risk of complications, pressure dressings are frequently applied to wounds. The actual pressures yielded by different dressing materials and application techniques have not been documented. OBJECTIVE: To measure and compare pressures produced using various types of dressing tapes with and without a gauze roll. METHODS: An infant blood pressure cuff was adapted for use in a pressure dressing model. Investigators independently applied four strips of each of five different types of tape to the cuff when it was located in three settings: a hard inanimate surface, a subject's distal volar forearm, and the subject's forehead. RESULTS: Foam and plastic tapes produced more pressure under a simple dressing than three other commonly used tapes. Higher, more consistent pressures were achieved on the forearm than the forehead. Adding a gauze roll to the dressing consistently increased the pressure. CONCLUSION: The experimental model demonstrated substantial differences in pressures yielded by various pressure dressing materials.

Analysis of Variance↗

PubMed1983

Inaccuracy of oesophageal pressure for pleural pressure estimation in supine anaesthetized subjects.

Oesophageal pressure was measured, using a balloon and catheter system, at three or four positions in the oesophagus of eight supine subjects anaesthetized with 1-1.5% halothane in 67% nitrous oxide. Airway pressure and the difference between airway and oesophageal pressures were recorded during occlusion of inspiration, occlusion of expiration and occlusion of expiration followed by inspiratory occlusion. Lung volume could not change appreciably during these manoeuvres, so the difference between airway and oesophageal pressure should not have changed. The change in oesophageal pressure was less than the change in airway pressure in 86 of 90 measurements. The change in oesophageal pressure was expressed as a fraction of the change in airway pressure: the maximum fraction was obtained in each patient, and the mean of these maximum values was 82%. This suggests that changes in the difference between airway and oesophageal pressures will overestimate the change in transpulmonary pressure during artificial ventilation in supine subjects, and that lung compliance would be underestimated.

Adult↗

PubMed1999

Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position.

We have compared ease of insertion, oropharyngeal leak pressure, directly measured pharyngeal mucosal pressure and anatomical position (assessed fibreoptically) for the size 4 and size 5 laryngeal mask airway (LMA) in 20 male and 20 female patients. Microchip pressure sensors were attached to the LMA at locations corresponding to the piriform fossa, hypopharynx, base of the tongue, lateral and posterior pharynx, and the oropharynx. Oropharyngeal leak pressure, mucosal pressure and fibreoptic position were recorded during inflation of the cuff from 0 to 30 ml in 10-ml increments. In males, oropharyngeal leak pressure over the inflation range was higher for size 5 (21 vs 17 cm H2O; P = 0.01); mucosal pressure over the inflation range was higher in the posterior pharynx for size 4 (7 vs 2 cm H2O; P = 0.007), and higher in the piriform fossa (8 vs 5 cm H2O; P = 0.003) and hypopharynx (9 vs 5 cm H2O; P = 0.003) for size 5. In females, oropharyngeal leak pressure over the inflation range was the same (21 vs 21 cm H2O), but mucosal pressure over the inflation range was higher in the piriform fossa (21 vs 8 cm H2O; P = 0.003) and posterior pharynx (4 vs 2 cm H2O; P = 0.004) for size 4, and higher in the lateral pharynx (5 vs 1 cm H2O; P = 0.01) and oropharynx (11 vs 5 cm H2O; P = 0.009) for size 5. The distribution of mucosal pressure was different for size 4 between males and females, but not for size 5. For both males and females, fibreoptic position was similar. We conclude that the size 5 LMA is optimal in males, but either size is suitable for females. The shape of the pharynx may be different between males and females.

Adult↗

PubMed1982

Left ventricular O2 requirements of pressure and volume loading in the normal canine heart and inaccuracy of pressure-derived indices of O2 demand.

The purpose of this study was to: 1) re-evaluate the left ventricular O2 requirements (MVO2) of pressure and volume-loading; and b) assess the accuracy of pressure-derived indices of left ventricular (LV) O2 demand under pressure-loading and volume-loading conditions. Using a right heart bypass preparation (heart rate 150 beats . min-1), mean arterial pressure (7.3 to 22.9 kPa) and cardiac output (0.8 to 6.0 litre . min-1) were varied independently. Adequate left ventricular O2 supply was demonstrated by normal transmural distribution of blood flow, normal myocardial lactate metabolism, and intact reactive hyperaemic responses. For equivalent increases in cardiac external work (from 2 to 4 joules . min-1) pressure-loading and volume-loading resulted in similar increases in O2 uptake (59% and 49%, respectively, P = 0.21). MVO2 was consistently greater for volume-loading than for pressure-loading at any SPTI, pressure-rate product, and triple product. The prediction of O2 demands by these indices under these loading conditions collectively was unreliable (r = 30 to 0.42). O2 requirements of the left ventricle with both pressure-loading and volume-loading were highly correlated (r = 0.82 to 0.99) with meridional wall stress. We conclude that: 1) volume-loading conditions have a greater O2 requirement than appreciated previously; 2) pressure loads and volume loads require similar O2 uptake in the normal canine heart for similar external work; 3) currently used pressure-derived indices are unreliable predictors of LV O2 demand when loading conditions are varied; and 4) O2 requirements are more uniformly related to meridional wall stress.

Animals↗

PubMed1991

Non-uniform and non-linear end systolic pressure-length relations at low left ventricular pressures in anaesthetised cats.

STUDY OBJECTIVE: The aims were (1) to establish a basis for measurements of regional inotropy using the slope (E) of the linear part of the end systolic pressure-length relation; (2) to investigate the range of end systolic pressure where linearity is valid, and particularly its lower pressure limit, called turning point pressure; (3) to determine whether local myocardial inotropy measured by normalised slope, E(n), varies with segment orientation DESIGN: Pressure and two cross oriented segment lengths were measured in the left ventricle. One pair of crystals measured a longitudinal segment, aligned with anterior midwall fibre direction; another pair measured a transverse segment, aligned with endocardial and epicardial fibre direction. Temporary obstruction of the inferior caval vein and descending aorta were performed to produce a wide pressure range of end systolic pressure-length relations during basal as well as high inotropic states (isoprenaline). SUBJECTS: Seven open chest cats anaesthetised with sodium pentobarbitone and nitrous oxide were used. MEASUREMENTS AND MAIN RESULTS - Turning point pressure for longitudinal segments showed lower values than for transverse segments (p less than 0.05). With isoprenaline, turning point pressure increased for all transverse segments, at 103(SEM 8) v 153(19) mm Hg (p less than 0.05), whereas no change occurred for longitudinal segments, at 82(4) v 87(7) mm Hg. In the basal state, E(n) showed lower values in all longitudinal segments compared to transverse segments, except for one pair. E(n) of all segments increased during isoprenaline infusion, except in one segment where no change occurred. CONCLUSIONS - There is a lower limit for linearity of end systolic pressure-length relations; this is affected by segment orientation as well as by the inotropic state of the heart. E(n) as a measure of regional inotropy varies with segment orientation, but offers a local measure of changes in inotropic state.

Anesthesia, General↗

PubMed1998

Progression of diabetic nephropathy--is diurnal blood pressure rhythm as important as absolute blood pressure level?

BACKGROUND: Hypertensive non-diabetic patients who lack the normal nocturnal decline in blood pressure ('non-dippers') have an increased incidence of cardiovascular complications. Poor blood pressure control is known to exacerbate the decline in glomerular filtration rate in patients with diabetic nephropathy. METHODS: The aim of this study was to assess the contribution of abnormal blood pressure diurnal rhythm to the progression of diabetic nephropathy. We retrospectively studied 26 diabetic patients with hypertension, proteinuria and relentless progressive impairment of renal function due to diabetic nephropathy between 1990 and 1996. Patients underwent ambulatory blood pressure monitoring and were classified as either 'dippers' or 'non-dippers' according to their blood pressure diurnal rhythm. Dippers were patients whose mean sleeping blood pressure (both systolic and diastolic) was 10% less than blood pressure whilst awake. Weight, glycated haemoglobin, serum creatinine (micromol/l) and blood pressure (mmHg) were recorded on a 3-monthly basis. Twenty four hour urine protein excretion and creatinine clearance were recorded annually. The rate of decline of creatinine clearance was derived from serum creatinine estimation. RESULTS: In the 'dipper' group, the rate of decline of creatinine clearance was -2.9 ml/min/year and in those with abnormal blood pressure diurnal rhythm it was -7.9 ml/min/year (P<0.05). There was no significant difference in day-time mean blood pressures, glycated haemoglobin, age and numbers with insulin-dependent diabetes mellitus. CONCLUSION: We found that there was a profound effect of non-dipping upon the rate of decline of renal function in patients with diabetic nephropathy.

Adult↗

PubMed1986

Aggregation of blood pressure in the families of children with labile high systolic blood pressure. The Muscatine Study.

The aggregation of systolic blood pressure, diastolic blood pressure, and heart rate is compared among the relatives of three groups of index children: children with low systolic blood pressure (less than the 5th percentile), middle range systolic blood pressure (between the 5th and 95th percentiles), or labile high blood pressure (above the 95th percentile when first sampled but below the 95th percentile when resampled four to six months later). Both systolic and diastolic blood pressures aggregate more strongly in the families of children with labile high systolic blood pressure than in the families of children with middle or low range systolic blood pressure. The degree of aggregation of heart rate does not differ among the three groups. Since blood pressures aggregate so strongly in families of children with labile high systolic blood pressure, study of these children and their families may yield important information about the etiology of hypertension.

Adolescent↗

PubMed1982

Critical closing pressure, local perfusion pressure, and the failing skin flap.

A simple apparatus was devised to perfuse the rat groin flap to study the relationship between perfusion pressure and flow. Results demonstrate that a relatively high intraarterial pressure must be applied to this skin flap before blood flow will commence. Results suggest that this critical closing phenomenon is the result of surface tension, blood rheology, venous pressure, tissue pressure, and vascular smooth muscle tone. Correlating the experiments of Milton and Landis reveals that, beyond a certain distance, local perfusion pressure in a skin flap gradually decreases with increasing distance from the flap base. These observations suggest that the perfusion boundary in a skin flap forms at the point where perfusion pressure has fallen to the level of the critical closing pressure. Methods of increasing survival length of a flap by decreasing critical closing pressure are discussed. The effects of edema and pressure dressings on flap and replant survival are examined in terms of the closing pressure concept.

Animals↗

PubMedDate not supplied

Effect of shoe modifications on center of pressure and in-shoe plantar pressures.

This study was conducted to determine the effect of footwear modification on patients with neuromusculoskeletal disorders. Two analyses, the center of pressure and the in-shoe plantar pressures, were studied with the help of healthy volunteers so that the effect of shoe modifications could be assessed. The ground force under the sole of the shoe was measured while the subjects were walking, and the plantar pressure at the foot-insole interface and its distribution were measured while the subjects were in both the standing and walking positions, wearing the trial shoes. The trial shoes had three different types of heels-standard heel, Thomas heel, and reverse Thomas heel-and had three different locations for the rocker bar--just under the metatarsophalangeal joint, 1 cm behind the metatarsophalangeal joint, and 1 cm before the metatarsophalangeal joint. The shift change at the center of pressure showed that the Thomas heel generally pushed the center of pressure more laterally and the reverse Thomas heel shifted it medially more than the standard heel did. While the subjects were in a stable standing position wearing the Thomas heel shoes, the medial forefoot and the lateral heel region's pressure showed significant reduction in the plantar pressure and the lateral forefoot and the medial heel showed a tendency to rise, compared with the standard heel condition. When the trial shoes' heels were changed to the reverse Thomas heel, the above changes tended to reverse. Tests at the foot-insole interface showed that the different types of heels and the location of the bar could change not only the pressure distribution but also the duration of the plantar pressure under the lateral area that shifted to the medial area when the subjects walked. This pressure measurement method was very useful for the design and evaluation of such footwear.

Adult↗

PubMed1997

Intratracheal pressure monitoring during synchronized intermittent mandatory ventilation and pressure controlled-inverse ratio ventilation.

OBJECTIVES: To directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator. DESIGN: Prospective, nonrandomized study. SETTING: Surgical intensive care unit at a trauma center. PATIENTS: Group 1: Eight intubated adult patients connected to mechanical ventilators in the SIMV mode were studied. All patients required mechanical ventilation following traumatic injuries. Group 2: Five intubated adult patients with adult respiratory distress syndrome connected to mechanical ventilators were studied. INTERVENTIONS: A small polyethylene catheter was threaded through each endotracheal tube such that it could be positioned to measure pressures proximal and distal to the tubes. MEASUREMENTS AND MAIN RESULTS: During SIMV, a significant pressure gradient exists across endotracheal tubes. In addition, although initiation of PC-IRV did lead to a lower peak airway pressure measured proximally, intratracheal peak airway pressure was unchanged. CONCLUSIONS: A pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.

Adult↗