Ratio Of Physiologic Dead Space Research Articles

The effect of surgical technique on hemodynamics, arterial oxygenation and pulmonary mechanics in radical prostatectomy operations.

The effects of surgical technique on respiratory mechanics, arterial oxygenation and hemodynamics in radical prostatectomy operation were investigated. The study was planned on ASA II-III, 40-65 years old, fourty patients scheduled for radical prostatectomy under general anesthesia. They were divided into two groups: perineal and suprapubic (Group P, n = 20; Group S, n = 20). Heart rate, mean arterial blood pressure, arterial oxygen saturation (SpO2), partial pressure of end-tidal carbon dioxide (PEtCO2), Peak inspiratory pressure (PIP), plato pressure (Pplato), partial pressure of oxygen in arterial blood (PaO2), partial pressure of carbon dioxide in arterial blood (PaCO2) values were evaluated at 10 minutes after induction. After the position applied for surgery in the 30.60 and 90th minutes, the Alveolar-arterial oxygen pressure gradient (P(A-a) O2), the ratio of physiologic dead space over tidal volume (VD/VT), arterial to end tidal CO2 gradient (P(a-et) CO2), static compliance (CS), dynamic compliance (CD) were assessed. In the assessment of groups, there were not statistical differences about mean blood pressure, heart rate, SpO2, PetCO2, PaO2, plateau pressure, and P (A-a) values (p > 0.05). Peak inspiratory pressure was higher in Group P. Peak inspiratory pressure and plateau pressure increased with CO2 insufflation in Group P. PaCO2 and P(a-et) CO2 were higher statistically significantly in Group 0. There was no difference in terms of the PetCO2 values. VD/VT ratios were statistically significantly lower in the Group P. Suprapubic surgery was shown to improve oxygenation and respiratory mechanics without causing any hemodynamic side effect in radical prostatectomy operation.

SELECTION OF RECIPIENTS FOR HEART TRANSPLANTATION BASED ON URGENCY STATUS

The article provides the overview of current international recommendations dedicated to selection of heart transplantation recipients based on urgency status. Authors found that cardiopulmonary bicycle stress test allowed to reveal additional criteria of high death risk within 1 year. These additional criteria were: the maximal oxygen consumption VO2max < 30% of the expected considering the age; VD/VT (ratio of physiologic dead space over tidal volume) increasing during the test; maximal tolerance to physical loading ≤50 Wt and/or < 20% of the expected considering the age. Authors created mathematical model for prediction of death within 1 year based on above mentioned data. Special software estimating the probability of death within 1 year was also created.

The effects of 10 cmH 2 O positive end-expiratory pressure on arterial oxygenation, respiratory mechanics and hemodynamic parameters in laparoscopic cholecystectomy operations

Objective: The effects of 10cmH2O Positive End-expiratory Pressure (PEEP) on respiratory mechanics, arterial oxygenation and hemodynamics in laparoscopic cholecystectomy operation were investigated. Methods: The study was planned on ASA I-II, 18-65 years old, forty patients scheduled for laparoscopic cholecystectomy under general anesthesia. The patients were divided into two groups which PEEP implemented Group 0 and 10 cmH2O PEEP applied Group P (Group 0, n=20; Group P, n=20). Heart rate, Mean arterial blood pressure, arterial oxygen saturation (SpO2), partial pressure of end-tidal carbon dioxide (PEtCO2), Peak inspiratory pressure (PİP), plato pressure (Pplato), partial pressure of oxygen in arterial blood (PaO2), partial pressure of carbon dioxide in arterial blood (PaCO2 ) values were evaluated at 5 minutes after induction, 5 minutes after CO2 insufflation, after the head-up position and the right side in the 10th and 30th minutes, After 10 minutes desufflation and in the recovery room. The Alveolar–arterial oxygen pressure gradient (P(A-a) O2), the ratio of physiologic dead space over tidal volume (VD/VT), Arterial to End Tidal CO2 gradient (P(a-et) CO2), static compliance (CS), dynamic compliance (CD) were assessed same times. Results: The assessment between the groups, there were not statistical differences about mean blood pressure, heart rate, SpO2, PetCO2, PaO2, plateau pressure, and P (A-a) values (p>0.05). Peak inspiratory pressure was higher in Group P (p<0.05). Peak inspiratory pressure and plateau pressure increased with CO2 insufflation in both groups. PaCO2 and P(a-et) CO2 were higher statistically significantly in Group 0 (p<0.05). There was no difference between the groups in terms of the PetCO2 values. VD/VT ratios were statistically significantly lower in the Group P (p<0.05). There was no difference at static compliance values between the groups, dynamic compliance was lower in Group P. According to the initial values, there was a decrease in compliance in both groups after CO2 insufflation. Conclusion: 10 cmH2O PEEP was shown to improve oxygenation and respiratory mechanics without causing any hemodynamic side effect in laparoscopic cholecystectomy operation.

Pulmonary dead space in free-ranging immobilized black rhinoceroses (Diceros bicornis) in Namibia.

It was observed previously that end-expired carbon dioxide (P(E)CO2) decreased when immobilized black rhinoceroses (Diceros bicornis) were moved from sternal to lateral recumbency. These experiments were designed to test whether greater alveolar ventilation or greater pulmonary dead space in lateral recumbency explains this postural difference in P(E)CO2. Twenty-one (9 male, 12 female; 15 [3.5-26] yr old) wild black rhinoceroses were immobilized with etorphine and azaperone and positioned in either sternal or lateral recumbency. All rhinoceroses were hypoxemic and had lactic and respiratory acidemia. The animals in lateral recumbency were more acidemic, had higher lactate, and lower arterial oxygen that those in sternal recumbency; however, arterial carbon dioxide was similar between groups. Both P(E)CO2 and mixed expired carbon dioxide pressure were lower in lateral than sternal recumbency. Although there was no difference in tidal volume or arterial carbon dioxide, both the breathing rate and minute ventilation were greater in lateral recumbency. The physiologic dead space ratio and dead space volume were approximately two times larger in lateral recumbency; hence, the decrease in P(E)CO2 in lateral recumbency can be attributed to increased dead space ventilation not increased alveolar ventilation. Positioning immobilized rhinoceroses in lateral recumbency does not confer any advantage over sternal in terms of ventilation, and the increase in minute ventilation in lateral recumbency can be considered an energetic waste. Although arterial oxygen was superior in sternal recumbency, further studies that measure oxygen delivery (e.g., to the muscles of locomotion) are warranted before advice regarding the optimal position for immobilized rhinoceroses can be given with confidence.

Effects of inspired oxygen concentration on ventilation, ventilatory rhythm, and gas exchange in isoflurane-anesthetized horses

To compare the effects of 2 fractions of inspired oxygen, 50% and > 95%, on ventilation, ventilatory rhythm, and gas exchange in isoflurane-anesthetized horses. 8 healthy adult horses. In a crossover study design, horses were assigned to undergo each of 2 anesthetic sessions in random order, with 1 week separating the sessions. In each session, horses were sedated with xylazine hydrochloride (1.0 mg/kg, IV) and anesthesia was induced via IV administration of diazepam (0.05 mg/kg) and ketamine (2.2 mg/kg) Anesthesia was subsequently maintained with isoflurane in 50% or > 95% oxygen for 90 minutes. Measurements obtained during anesthesia included inspiratory and expiratory peak flow and duration, tidal volume, respiratory frequency, end-tidal CO(2) concentration, mixed expired partial pressures of CO(2) and O(2), PaO(2), PaCO(2), blood pH, arterial O(2) saturation, heart rate, and arterial blood pressure. Calculated values included the alveolar partial pressure of oxygen, alveolar-to-arterial oxygen tension gradient (PaO(2) - PaO(2)), rate of change of PAO(2) - PaO(2), and physiologic dead space ratio. Ventilatory rhythm, based on respiratory rate and duration of apnea, was continuously observed and recorded. Use of the lower inspired oxygen fraction of 50% resulted in a lower arterial oxygen saturation and PaO(2) than did use of the higher fraction. No significant difference in PaCO(2), rate of change of PAO(2) - PaO(2), ventilatory rhythm, or other measured variables was observed between the 2 sessions. Use of 50% inspired oxygen did not improve the ventilatory rhythm or gas exchange and increased the risk of hypoxemia in spontaneously breathing horses during isoflurane anesthesia. Use of both inspired oxygen fractions requires adequate monitoring and the capacity for mechanical ventilation.

Vagal nerve activity contributes to improve the efficiency of pulmonary gas exchange in hypoxic humans

The aim of this study was to test our hypothesis that both phasic cardiac vagal activity and tonic pulmonary vagal activity, estimated as respiratory sinus arrhythmia (RSA) and anatomical dead space volume, respectively, contribute to improve the efficiency of pulmonary gas exchange in humans. We examined the effect of blocking vagal nerve activity with atropine on pulmonary gas exchange. Ten healthy volunteers inhaled hypoxic gas with constant tidal volume and respiratory frequency through a respiratory circuit with a respiratory analyser. Arterial partial pressure of O(2) (P(aO(2))) and arterial oxygen saturation (S(pO(2))) were measured, and alveolar-to-arterial P(O(2)) difference (D(A-aO(2))) was calculated. Anatomical dead space (V(D,an)), alveolar dead space (V(D,alv)) and the ratio of physiological dead space to tidal volume (V(D,phys)/V(T)) were measured. Electrocardiogram was recorded, and the amplitude of R-R interval variability in the high-frequency component (RRIHF) was utilized as an index of RSA magnitude. These parameters of pulmonary function were measured before and after administration of atropine (0.02 mg kg(-1)). Decreased RRIHF (P < 0.01) was accompanied by decreases in P(aO(2)) and S(pO(2)) (P < 0.05 and P < 0.01, respectively) and an increase in D(A-aO(2)) (P < 0.05). Anatomical dead space, V(D,alv) and V(D,phys)/V(T) increased (P < 0.01, P < 0.05 and P < 0.01, respectively) after atropine administration. The blockade of the vagal nerve with atropine resulted in an increase in V(D,an) and V(D,alv) and a deterioration of pulmonary oxygenation, accompanied by attenuation of RSA. Our findings suggest that both phasic cardiac and tonic pulmonary vagal nerve activity contribute to improve the efficiency of pulmonary gas exchange in hypoxic conscious humans.

Impact of Mechanical Ventilation on the Developing Airway

After completing this article, readers should be able to: 1. Explain why immature infants are at a greater risk for mechanical ventilation-induced airway damage than are more mature infants. 2. Describe the effect of ventilatory pressures on components of the airway. 3. Delineate how mechanical ventilation disrupts airway mechanics. 4. Characterize how mechanical ventilation affects immature airway smooth muscle. 5. Describe techniques of optimizing ventilation to minimize respiratory damage. Although the air passages take on a mature appearance well before a fetus is viable, they undergo significant maturational changes in late gestation. During development, the airways are more susceptible to damage. In fact, although controversy still surrounds the pathogenesis of bronchopulmonary dysplasia (BPD) and other neonatal airway complications, it appears that the duration and higher pressures of mechanical ventilation, along with the use of oxygen, are related to the development of airway-related problems in preterm infants. As a result, because of their greater need for ventilatory assistance, very preterm infants are at substantially increased risk of airway damage. With recent and continuing advancements in neonatal care, a growing number of immature infants survive premature births. One of the primary hurdles that must be overcome in these infants is respiratory system immaturity. In this context, an understanding of the embryologic development and physiologic maturation of the respiratory system is imperative. The respiratory system can be subdivided grossly into the airways and the lung parenchyma. Developmental changes in the mechanical properties of these two components predispose the immature airway to injury. The immature lung is a relatively noncompliant structure. During neonatal development, lung compliance increases with lung maturity. However, the opposite is true for airways. Immature airways are relatively more compliant than their mature counterparts, with airway maturation resulting in a decrease in airway compliance. This produces an interesting predicament when contemplating the administration of mechanical ventilation …

The Relationship between End Tidal Carbon Dioxide and Arterial Carbon Dioxide during Controlled Hypotensive Anaesthesia

Objectives: To prospectively assess the magnitude of changes in the arterial-to-end tidal carbon dioxide gradient [P(a-ET)CO₂] as well as in the ratio of physiological dead space to tidal volume (Vd_phys/Vt) during controlled hypotensive anaesthesia, and to evaluate whether or not ventilatory requirements remain unaltered during this procedure. Subjects and Methods: Twelve adult patients with American Society of Anesthesiologists’ physical status I and II undergoing middle ear surgery were selected. A standard anaesthetic procedure was followed for all cases, using thiopental sodium, succinylcholine, fentanyl, atracurium and 60% N₂O in 40% oxygen supplemented with isoflurane. Mean arterial blood pressure (MAP) was reduced to 60 ± 5 mm Hg in all patients using a sodium nitroprusside infusion. The end tidal (ET) CO₂, PaCO₂, MAP, peak airway pressure, plateau pressure and expiratory minute volume were recorded during a period of normal arterial blood pressure (time 1) and during hypotension (time 2). Results: A significant decrease in PaCO₂ (7%) and ETCO₂ (17%) from time 1 to time 2 (p < 0.01) was noted, as was a significant increase in P(a-ET)CO₂ (48%) and in the Vd_phys/Vt ratio (41.17%) (p < 0.01) during the same period. Conclusion: The decrease in ETCO₂ does not reflect the changes in PaCO₂. The larger decrease in ETCO₂ is mainly due to the increase in the Vd_phys/Vt ratio. During anaesthesia, once normocapnia is achieved with normal arterial blood pressure, there is hardly any need to change the ventilation after initiation of controlled hypotension.

Significance of End-Tidal Pco2 Response to Exercise and Its Relation to Functional Capacity in Patients With Chronic Heart Failure

The value of end-tidal PCO(2) monitoring during exercise in patients with chronic heart failure has not been elucidated. The present study was designed to examine end-tidal PCO(2) response to exercise and its relation to functional capacity in patients with chronic heart failure. Maximal upright ergometer exercise with respiratory gas analysis and arterial blood gas analysis were performed in 105 patients with chronic heart failure (34 patients in New York Heart Association [NYHA] class I, 38 patients in NYHA class II, and 33 patients in NYHA class III) and 14 normal control subjects. Peak O(2) uptake, excessive exercise ventilation as assessed by the slope of the relation between expired minute ventilation and CO(2) output (VE-VCO(2)), and the ratio of physiologic dead space to tidal volume (VD/VT) were determined. Cardiac output was also measured during exercise in 28 patients with chronic heart failure. Arterial PO(2) or PCO(2) values at rest and during exercise were not different among the four groups. However, end-tidal PCO(2) was significantly lower, and arterial to end-tidal PCO(2) difference and VD/VT were significantly higher in NYHA class III patients than other groups during exercise. The maximal end-tidal PCO(2) during exercise was significantly reduced as the severity of chronic heart failure advanced (45.7 +/- 4.0 mm Hg in normal control subjects, 43.5 +/- 4.8 mm Hg in NYHA class I patients, 39.7 +/- 5.1 mm Hg in NYHA class II patients, and 34.9 +/- 5.3 mm Hg in NYHA class III patients). The maximal end-tidal PCO(2) during exercise was significantly correlated with peak O(2) uptake (r = 0.68; p < 0.001) and maximal cardiac index (r = 0.73; p < 0.001), and inversely related to Ve-VCO(2) (r = - 0.84; p < 0.001) and VD/VT at peak exercise (r = -0.65; p < 0.001). The decreased end-tidal PCO(2) during exercise, which is caused by high ventilation/perfusion ratio mismatching, reflects both reduced cardiac output response to exercise and increased exercise ventilation due to enlarged physiologic dead space in advanced chronic heart failure. The end-tidal PCO(2) during exercise can be used to evaluate the functional capacity of patients with chronic heart failure.

The Correlation between HRCT Emphysema Score and Exercise Pulmonary Testing Parameters

Background The correlation between the high resolution computed tomography(HRCT) emphysema score and the physiologic parameters including resting and exercise pulmonary function test was investingated in 14 patients(60.6±10.3 years) with pulmonary emphysema. Methods The patients underwent a HRCT, a resting pulmonary function test, and incremental exercise testing(cycle ergometer, 10 W/min). Computed tomography scans were obtained on a GE highlight at 10 mm intervals using 10 mm collimation, from the apex to the base after a full inspiration. The emphysema scores wer determined by a CT program 'Density mask' outlining the areas with attenuation values less than -900 HU, indicating the emphysema areas, and providing an overall percentage of lung involvement by emphysema. Results Among the resing PFT parameters, only the diffusing capacity(r=-0.75) and PaO2 (r=-0.66) correlated with the emphysema score(p<0.05). Among the exercise test parameers, the emphysema score correlated significantly with the maximum power(r=-0.74), maximum oxygen consumption(r=-0.68), anaerobic threshold(V-slope method : r=-0.69), maximal O2-pulse(r=-0.73), and the physiologic dead space ratio at the maximum workload(r=-0.80)(p<0.01). Conclusion We could find that exercise testing parameters showed a much better correlation with the HRCT emphysema score, which is known to have a good correlation with the pathologic severity than the resting PFT parameters. Therefore it is suggested that exercise testing is superior to resting PFT for estimating in the estimation of the physiologic disturbance in emphysema patients.

End-tidal CO2 pressure decreases during exercise in cardiac patients: Association with severity of heart failure and cardiac output reserve

OBJECTIVESWe measured end-tidal CO2 pressure (PETCO2) during exercise and investigated the relationship between PETCO2 and exercise capacity, ventilatory parameters and cardiac output to determine the mechanism(s) of changes in this parameter.BACKGROUNDIt is unclear whether PETCO2 is abnormal at rest and during exercise in cardiac patients.METHODSCardiac patients (n = 112) and normal individuals (n = 29) performed exercise tests with breath-by-breath gas analysis, and measurement of cardiac output and arterial blood gases.RESULTSPETCO2 was lower in patients than in normal subjects at rest and decreased as the New York Heart Association class increased, whereas the partial pressure of arterial CO2 did not differ among groups. Although PETCO2 increased during exercise in patients, it remained lower than in normal subjects. PETCO2 in relation to cardiac output was similar in patients and normal subjects. PETCO2 at the respiratory compensation point was positively correlated with the O2 uptake (r = 0.583, p < 0.0001) and the cardiac index at peak exercise (r = 0.582, p < 0.0001), and was negatively correlated with the ratio of physiological dead space to the tidal volume. The sensitivity and specificity of PETCO2 to predict an inadequate cardiac output were 76.6% and 75%, respectively, when PETCO2 at respiratory compensation point and a cardiac index at peak exercise that were less than the respective control mean–2 SD values were considered to be abnormal.CONCLUSIONSPETCO2 was below normal in cardiac patients at rest and during exercise. PETCO2 was correlated with exercise capacity and cardiac output during exercise, and the sensitivity and specificity of PETCO2 regarding decreased cardiac output were good. PETCO2 may be a new ventilatory abnormality marker that reflects impaired cardiac output response to exercise in cardiac patients diagnosed with heart failure.

Respiratory sinus arrhythmia. A phenomenon improving pulmonary gas exchange and circulatory efficiency.

The primary mechanisms of respiratory sinus arrhythmia (RSA) are understood to be the modulation of cardiac vagal efferent activity by the central respiratory drive and the lung inflation reflex, and the degree of RSA increases with cardiac vagal activity. However, it is unclear whether RSA serves an active physiological role or merely reflects a passive cardiovascular response to respiratory input. We hypothesized that RSA benefits pulmonary gas exchange by matching perfusion to ventilation within each respiratory cycle. In seven anesthetized dogs, a model stimulating RSA was made. After elimination of endogenous autonomic activities, respiration-linked heartbeat fluctuations were generated by electrical stimulation of the right cervical vagus during negative pressure ventilation produced by phrenic nerve stimulation (diaphragm pacing). The vagal stimulation was performed in three conditions; phasic stimulation during expiration (artificial RSA) and during inspiration (inverse RSA) and constant stimulation (control) causing the same number of heartbeats per minute as the phasic stimulations. Although tidal volume, cardiac output, and arterial blood pressure were unchanged, artificial RSA decreased the ratio of physiological dead space to tidal volume (VD/VT) and the fraction of intrapulmonary shunt (Qap/Qt) by 10% and 51%, respectively, and increased O2 consumption by 4% compared with control. Conversely, reverse RSA increased VD/VT and Qap/Qt by 14% and 64%, respectively, and decreased O2 consumption by 14%. These results support our hypothesis that RSA benefits the pulmonary gas exchange and may improve the energy efficiency of pulmonary circulation by "saving heartbeats."

Effect of two tidal volumes on oxygenation and respiratory system mechanics during the early stage of adult respiratory distress syndrome

Purpose: To study the effect of two tidal volumes on gas exchange, lung mechanics, and hemodynamics in 12 patients with acute respiratory distress syndrome (ARDS) within the first 72 hours of mechanical ventilation. Methods: Tidal volume (VT) was increased by 40% from the initial value at fixed positive end-expiratory pressure (PEEP) and matched minute ventilation by adjusting the respiratory rate (RR) of the ventilator. Initial VT and RR were 592 ± 42 mL and 19 ± 1 min −1, respectively. High VT amounted to 825 ± 54 mL with a RR of 12 ± min −1. Results: We found that at high VT (1) the index of oxygenation increased from 0.22 ± 0.03 to 0.32 ± 0.04 ( P < .001) with a parallel decrease in the right to left venous admixture from 0.26 ± 0.02 to 0.23 ± 0.02 ( P < .001), and in the ratio of physiological dead space to tidal volume (V ds/V t) from 0.53 ± 0.05 to 0.46 ± 0.04 ( P < .01), without impairment to hemodynamics and (2) respiratory system compliance improved significantly from 34.8 ± 2.8 mL/cm H 2O to 37.2 ± 2.9 mL/cm H2O ( P < .05). In 4 patients, we performed pressure-volume curves on PEEP with the ventilator finding an upward concavity reflecting progressive alveolar recruitment with increasing inflation volume in 3. Conclusions: High-tidal ventilation in the early stage of ARDS improved gas exchange, suggesting recruitment during the inspiratory phase. However, the benefit of better oxygenation should be weighed against the potential risk of barotrauma induced at high V t.

Importance of abnormal lung perfusion in excessive exercise ventilation in chronic heart failure

Whether excessive ventilatory response to exercise is related to the maldistribution of pulmonary blood flow was examined in 23 patients with chronic heart failure and nine age-matched normal subjects. With the use of technetium 99m macroaggregated albumin, the resting distribution of pulmonary blood flow was assessed by the scintigraphic counts ratio of upper to lower lung fields. The ventilatory response to exercise was assessed by the slope of the relationship between minute ventilation and carbon dioxide production during exercise. Eight patients (group A) had slope less than 33, the upper limit of the normal range, and 15 patients had slope of 33 or greater (group B). In group B pulmonary blood flow was distributed more to the upper lung, which made the counts ratio (60%) higher than in normal subjects (34%) or in patients in group A (38%). There was no significant difference in pulmonary flow distribution between normal subjects and patients in group A. In group B tidal volume did not increase during exercise as much as it did in normal subjects and in patients in group A; therefore, the respiratory pattern was rapid and shallow. Although the ratio of physiologic dead space to tidal volume fell by 20% during exercise in normal subjects and by 23% in patients in group A, it failed to decrease in patients in group B (−1%), which indicates a relative increase in dead space respiration during exercise. These data indicate that decreased lung compliance and regional ventilation-perfusion mismatch caused by pulmonary vascular and parenchymal abnormalities would play an important role in the excessive exercise ventilation in chronic heart failure.

Pulmonary gas exchange and oxygen uptake during exercise in patients with type 1 diabetes mellitus.

In order to investigate pulmonary gas exchange and cardiopulmonary performance in Type 1 diabetes, 36 patients underwent a progressive incremental exercise test on a cycle ergometer. Cardiopulmonary variables were measured, and arterial blood gases determined on samples obtained from an indwelling catheter in the radial artery. The results were compared with those from 40 control subjects. In the patients, the maximum power (Wmax) and maximum oxygen uptake (VO2max) were lower than in the control subjects (Wmax 186 +/- 52 (+/- SD) vs 233 +/- 48 W, p less than 0.05; VO2max 2.56 +/- 0.71 vs 3.17 + 0.77 l min-1, p less than 0.05). At comparable levels of power output, however, no significant abnormality was observed in the difference between alveolar and arterial oxygen pressure (P(A-a)O2), and the ratio of physiological dead space to tidal volume (VD/VT ratio). These data indicate that in Type 1 diabetic patients, despite their reduced maximum oxygen uptake, gas transfer during exercise is not limited and thus does not contribute to the impairment of exercise capacity.

Early effects of inhalation injury on lung mechanics and pulmonary perfusion.

We investigated the early effects of a rather large amount of cotton-smoke on lung mechanics and pulmonary perfusion. Under halothane anesthesia 18 ewes were intubated with a double-lumen tube. In 6 sheep the left lung was exposed to smoke, in another 6 the right lung. A sham group of 6 sheep was insufflated with air instead of smoke. Prior to and 30-45 min following the smoking- (sham-) procedure the following parameters were determined for the smoke- (sham-) exposed and the contralateral lung: static compliance, inspiratory airway resistance, and physiologic dead space ratio. In addition MAP, MPAP, WP, and CO were recorded. The data indicate that inhalation of large amounts of smoke has no major direct effects on pulmonary mechanics and perfusion in the early post-injury period. Only an increase in airway resistance of the smoke exposed lungs was found, which must be attributed to a local reflex mechanism.

National survey of methods and criteria used for weaning from mechanical ventilation.

A national survey of hospital-based respiratory care departments was conducted to quantitate the use of various techniques and criteria employed to facilitate weaning of patients from mechanical ventilatory support. Responses were partitioned into private, nonprivate and university/university-affiliated institutions with further subdivision into bed-size groups of not more than 50 beds, 51 to 150 beds, 151 to 300 beds, and not less than 301 beds. Intermittent mandatory ventilation (IMV) was the most frequently used weaning technique in 90.2% of the responding hospitals. IMV was also listed as the primary mode of mechanical ventilatory support (71.6%). IMV to a T-tube system was the most common weaning protocol in nonuniversity hospitals. IMV to 3 to 5 cm H2O continuous positive airway pressure and IMV to T-tube were equally utilized in university/university-affiliated centers. PaCO2 was identified the most often (20.7%) and physiologic deadspace ratio the least often (2.5%) as a weaning criterion. We conclude that IMV is probably the most widely practiced weaning technique and that a variety of weaning criteria were employed.

EARLY EFFECTS OF INHALATION INJURY ON LUNG MECHANICS AND PULMONARY PERFUSION

We investigated the early effects of a rather large amount of cotton-smoke on lung mechanics and pulmonary perfusion. Under halothane anesthesia 18 ewes were intubated with a double-lumen tube. In 6 sheep the left lung was exposed to smoke, in another 6 the right lung. A sham group of 6 sheep was insufflated with air instead of smoke. Prior to and 30–45 min following the smoking- (sham-) procedure the following parameters were determined for the smoke- (sham-) exposed and the contralateral lung: static compliance, inspiratory airway resistance, and physiologic dead space ratio. In addition MAP, MPAP, WP, and CO were recorded. The data indicate that inhalation of large amounts of smoke has no major direct effects on pulmonary mechanics and perfusion in the early post-injury period. Only an increase in airway resistance of the smoke exposed lungs was found, which must be attributed to a local reflex mechanism.

Right Ventricular Stroke-Work: An Index of Distribution of Pulmonary Perfusion in Acute Respiratory Failure

To evaluate the possibility that an elevated right ventricular stroke-work index observed in acute respiratory failure correlates with less dead space ventilation, 20 patients requiring mechanical ventilation were studied. Ratio of physiologic dead space to tidal volume was used as an index of distribution of pulmonary perfusion. An inverse linear relationship was found between right ventricular stroke-work index and dead space ratio (r = -0.74, p less than 0.001). No correlation was present between cardiac index and dead space ratio. To evaluate the effects of other hemodynamic data on the distribution of pulmonary perfusion, the patients were divided into two groups based on a dead space ratio. Comparison of the two groups revealed right ventricular stroke-work index was significantly higher in the low dead space ratio group (p less than 0.001). There were no differences in cardiac index, pulmonary-artery pressure, or right atrial pressures. These data suggest that elevated right ventricular stroke-work index in acute respiratory failure is associated with more even distribution of pulmonary perfusion, and that patients with a high dead space ratio were characterized by right ventricular dysfunction when compared to patients with a low dead space ratio.

Physiologic Effects of Oral Bronchodilators during Rest and Exercise in Chronic Obstructive Pulmonary Disease

At rest and during exercise, noninvasive studies of cardiopulmonary physiology in patients with chronic obstructive pulmonary disease (COPD) were carried out to determine the objective benefits of commonly used oral bronchodilator drugs in 15 stable patients without cardiovascular disease or reversible obstruction of airflow. Theophylline, terbutaline, a combination of theophylline and terbutaline, and placebo were given for ten days each in a randomly sequenced double-blind protocol for outpatients. Spirometric values, the ratio of physiologic dead space to tidal volume (VDp/VT), and the alveolar-arterial oxygen pressure difference (P[A-a]O2) were studied at rest on each regimen. During steady-state exercise the changes in VDp/VT and P(A-a)O2, as well as the ventilatory equivalent for oxygen and oxygen pulse, were measured. When compared with placebo, no significant change was noted in the previously mentioned measurements with any regimen, with the exception of a small improvement in the forced expiratory volume in one second, which was significant for all regimens. These findings suggest that commonly used oral bronchodilator drugs in usual doses may have small effects on airflow even in "irreversible" COPD but that the objective effect of these agents on gas exchange during rest and exercise is not significant.