Alveolar-arterial Partial Pressure Difference Research Articles

Effects of pulsed inhaled nitric oxide delivery on the distribution of pulmonary perfusion in spontaneously breathing and mechanically ventilated anesthetized ponies.

To measure changes in pulmonary perfusion during pulsed inhaled nitric oxide (PiNO) delivery in anesthetized, spontaneously breathing and mechanically ventilated ponies positioned in dorsal recumbency. 6 adult ponies. Ponies were anesthetized, positioned in dorsal recumbency in a CT gantry, and allowed to breathe spontaneously. Pulmonary artery, right atrial, and facial artery catheters were placed. Analysis time points were baseline, after 30 minutes of PiNO, and 30 minutes after discontinuation of PiNO. At each time point, iodinated contrast medium was injected, and CT angiography was used to measure pulmonary perfusion. Thermodilution was used to measure cardiac output, and arterial and mixed venous blood samples were collected simultaneously and analyzed. Analyses were repeated while ponies were mechanically ventilated. During PiNO delivery, perfusion to aerated lung regions increased, perfusion to atelectatic lung regions decreased, arterial partial pressure of oxygen increased, and venous admixture and the alveolar-arterial difference in partial pressure of oxygen decreased. Changes in regional perfusion during PiNO delivery were more pronounced when ponies were spontaneously breathing than when they were mechanically ventilated. In anesthetized, dorsally recumbent ponies, PiNO delivery resulted in redistribution of pulmonary perfusion from dependent, atelectatic lung regions to nondependent aerated lung regions, leading to improvements in oxygenation. PiNO may offer a treatment option for impaired oxygenation induced by recumbency.

Alveolar-arterial partial pressure difference as an early predictor for patients with acute paraquat poisoning.

ObjectiveParaquat (PQ) is associated with high mortality rates in acute poisoning. This study aimed to determine the importance of the alveolar–arterial partial pressure difference (A-aDo2) in the expected consequences of acute PQ poisoning.MethodsPatients who were hospitalized for PQ poisoning in 2018 were enrolled in this retrospective study. A-aDo2 data were collected. Multivariate analysis was performed using binary logistic regression to determine whether A-aDo2 is an independent risk factor for mortality from PQ.ResultsA total of 352 cases were analyzed. The mean PQ dose was 36.84 ± 50.30 mL (0.3–500 mL). There were 185 survivors and 167 non-survivors. The mean A-aDo2 was not significantly correlated between survivors and non-survivors on day 1. However, there were significant differences in A-aDo2 between survivors and non-survivors on days 3, 7, 14, and 21. Increased A-aDo2 values were correlated with an increased mortality rate. The mean A-aDo2 on day 14 showed the most significant difference between survivors and non-survivors.ConclusionOur study suggests that A-aDo2 plays an important role as a reference index, which could be a useful predictor in assessing acute PQ poisoning, especially on the 14th day after onset of poisoning.

Deriving the arterial Po2 and oxygen deficit from expired gas and pulse oximetry.

The efficiency of pulmonary gas exchange is often assessed by the ideal alveolar-arterial partial pressure difference (A-aDO2). Through a combination of pulse oximetry and rapidly responding gas analyzers to measure the partial pressures of O2 and CO2 in expired gas, one can measure the oxygen deficit. Defined as the difference between the measured alveolar Po2 and the arterial Po2 calculated from , the oxygen deficit is a substitute for the alveolar-arterial Po2 difference. The oxygen deficit is physiologically reasonable in that it increases with age in healthy subjects and is well correlated with the A-aDO2. To calculate arterial Po2 from saturation, the saturation should be below the very flat upper part of the O2-Hb dissociation curve; good estimates can be made provided the arterial O2 saturation is below ~95%. Since saturations at or above 95% imply reasonably well-maintained gas exchange efficiency, this limitation is of only minor concern. Calculations show that it is necessary to take into account the change in Po2 at a saturation of 50% of the O2-Hb dissociation curve based on the measured alveolar Pco2. As the measurement is designed to be noninvasive, determination of any base excess is not practical, but calculations show that the effect of assuming a zero base excess is modest, with a similar small effect from an abnormal body temperature. Taken together, these results show that a noninvasive assessment of pulmonary gas exchange efficiency can be obtained from subjects with below-normal arterial O2 saturations through a combination of expired O2 and CO2 measurements and made during quiet breathing.NEW & NOTEWORTHY The details and limitations of a noninvasive measurement of pulmonary gas exchange efficiency, the oxygen deficit, are described. The oxygen deficit, calculated from expired gas measurements made during quiet breathing coupled with pulse oximetry, is a good surrogate measurement of the ideal alveolar-arterial Po2 difference and does not require arterial blood gas sampling.

Effect of net gas volume changes on alveolar and arterial gas partial pressures in the presence of ventilation-perfusion mismatch.

The second gas effect (SGE) occurs when nitrous oxide enhances the uptake of volatile anesthetics administered simultaneously. Recent work shows that the SGE is greater in blood than in the gas phase, that this is due to ventilation-perfusion mismatch, that as mismatch increases, the SGE increases in blood but is diminished in the gas phase, and that these effects persist well into the period of nitrous oxide maintenance anesthesia. These modifications of the SGE are most pronounced with the low soluble agents in current use. We investigate further the effect of net gas volume loss during nitrous oxide uptake on low concentrations of other gases present using partial pressure-solubility diagrams. The steady-state equations of gas exchange were solved assuming a log-normal distribution of ventilation-perfusion ratios using Lebesgue-Stieltjes integration. It was shown that under these conditions the classical partial pressure-solubility diagram must be modified, that for currently used volatile anesthetic agents the alveolar-arterial partial pressure difference is less than that predicted in the past, and that the alveolar-arterial partial pressure difference may even be reversed during uptake in the case of highly insoluble gases such as sulfur hexafluoride. Comparing this with the situation described previously for nitrogen in steady-state air breathing, we show that for nitrogen, the direction of the alveolar-arterial gradient is opposite to the direction of net gas volume movement. Although gas uptake with ventilation-perfusion inequality exceeding that when matching is optimal is shown to be possible, it is less likely than alveolar-arterial partial pressure reversal. NEW & NOTEWORTHY Net uptake of gases administered with nitrous oxide may proceed against an alveolar-arterial partial pressure gradient. The alveolar-arterial gradient for nitrogen in the steady-state breathing air depends not only on the existence of a distribution of ventilation-perfusion ratios in the lung but also on the presence of a net change in gas volume and is opposite in direction to the direction of net gas volume uptake.

Use of the oxygen content–based index, Fshunt, as an indicator of pulmonary venous admixture at various inspired oxygen fractions in anesthetized sheep

To evaluate the use of the oxygen content-based index, Fshunt, as an indicator of venous admixture (Qs/Qt) at various fractions of inspired oxygen (FIO(2)s) in anesthetized sheep undergoing Flung or 2-lung ventilation. Animals-6 healthy adult female sheep. Sheep were anesthetized and administered 5 different FIO(2)s (0.21, 0.40, 0.60, 0.80, and 1.00) in random order during 2-lung mechanical ventilation. Arterial and mixed venous blood samples were obtained at each FIO(2) after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used FIO(2) sequence was reversed for sample collection during Flung ventilation. Blood samples were analyzed for arterial, pulmonary end-capillary, and mixed venous oxygen content and partial pressure and for hemoglobin concentration. Oxygen hemoglobin saturation, Qs/Qt, Fshunt, and oxygen tension-based indices (OTIs; including PAO(2):FIO(2), alveolar-arterial difference in partial pressure of oxygen [PAO(2) - PAO(2)], [PAO(2) - Pao(2)]:FIO(2), [PAO(2) - PAO(2)]:PAO(2), and PAO(2):PAO(2)) were calculated at each FIO(2); associations were evaluated with linear regression analysis, concordance, and correlation tests. Intermethod agreement between Qs/Qt and Fshunt was tested via Bland-Altman analysis. Strong and significant associations and substantial agreement were detected between Fshunt and Qs/Qt. Relationships between OTIs and Qs/Qt varied, but overall correlations were weak. Conclusions and Clinical Relevance-Whereas OTIs were generally poor indicators of Qs/Qt, Fshunt was a good indicator of Qs/Qt at various FIO(2)s, regardless of the magnitude of Qs/Qt, and could be potentially used as a surrogate for Qs/Qt measurements in healthy sheep.

Experimental Study of Cardiorespiratory and Stress Factors in Esophageal Surgery Using Robot-Assisted Thoracoscopic or Open Thoracic Approach

Our aim was to compare cardiovascular and stress response to robotic technology during thoracoscopic mobilization and anastomosis of the esophagus vs the conventional open approach. Randomized experimental study. Department of Experimental Surgery, University of Heidelberg. Twelve pigs randomized to undergo robotic or conventional surgery (6 animals each). Fundus rotation gastroplasty followed by esophageal mobilization and intrathoracic anastomosis by conventional or robotic surgery. Mean arterial pressure, central venous pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, cardiac output, pulmonary vascular resistance, partial oxygen pressure, alveolar-arterial difference in partial pressure of oxygen, and arteriovenous oxygen content difference measured preoperatively, during esophageal manipulation, and 30 minutes after operation. Operative stress was assessed by plasma levels of cortisol and substance P. Hemodynamic measures showed higher intraoperative central venous pressure and pulmonary vascular resistance in the open surgery group, whereas cardiac output was significantly decreased compared with the robotic group. Blood gas values showed significant deterioration during esophageal manipulation with open surgery in contrast to the robotic group. Substance P and cortisol levels were significantly higher with the open approach. The robot-assisted approach is associated with improved intraoperative cardiopulmonary function and seems to be a less stressful technique.

High-Frequency Oscillatory Ventilation in Term and Near-Term Infants with Acute Respiratory Failure: Early Rescue Use

This study describes a high-frequency oscillatory ventilation (HFOV) protocol for term and near-term infants with acute respiratory failure (ARF) and reports results of its prospective application. Neonates, with gestational age >or= 34 weeks, were managed with HFOV, if required, on conventional ventilation (CV), a fraction of inspired oxygen (F IO(2)) 0.5, and a mean airway pressure > 10 cm H (2)O to maintain adequate oxygenation or a peak inspiratory pressure > 24 cm H (2)O to maintain tidal volume between 5 and 7 mL/kg of body weight. Seventy-seven infants (gestational age, 37 +/- 2,3 weeks), received HFOV after a mean duration of CV of 7.5 +/- 9.7 hours. Arterial blood gases, oxygenation index (OI), and alveolar-arterial difference in partial pressure of oxygen (P AO(2) - Pa O(2)) were recorded prospectively before and during HFOV. There were a rapid and sustained decreases in mean airway pressure (MAP), F IO(2), OI, and P AO(2) - Pa O(2) during HFOV ( P <or= 0.01). Seventy infants (91%) were weaned successfully from HFOV. Seven infants (P AO(2) - Pa O(2) prior to HFOV, 601 +/- 89 mm Hg) were classified as having experienced treatment failure and died from their underlying disease. Treatment failure was associated with lack of improvement in P AO(2) - Pa O(2) at 1 hour of HFOV ( P < 0.01). Early rescue intervention with HFOV is an effective protocol for term and near-term infants with ARF. Failure to improve P AO(2) - Pa O(2) rapidly on HFOV is associated with HFOV failure. Randomized controlled trials are needed to identify benefits of HFOV versus conventional modes of mechanical ventilation.

Ex Vivo Evaluation of Human Lungs for Transplant Suitability

If lungs could be retrieved from non-heart-beating donors, the critical shortage of lungs for transplant could be alleviated. An obstacle to this approach is the inability to predict these lungs' suitability for transplant. We used human lungs deemed unsuitable for transplant to develop a method to perfuse and ventilate human lungs ex vivo to assess gas exchange and vascular resistance, and to perform bronchoscopic inspection and radiographic evaluation. Lungs were retrieved from six brain-dead organ donors after cold Perfadex (Vitrolife, Kungsbacka, Sweden) flush, stored cold for 6 to 13 hours (mean, 8.7 hours) then perfused and rewarmed in a modified cardiopulmonary bypass circuit. Circuit perfusate was buffered colloid-crystalloid containing type-specific leukocyte-filtered blood (hematocrit of 10%-12%), circulated through a membrane oxygenator ventilated with CO2 and nitrogen to deoxygenate it. Lungs were ventilated with fraction of inspired oxygen (Fio2) 0.5 when 32 degrees C was reached. Gas exchange and vascular resistance was assessed at 5 L/minute flow at 37 degrees C, Fio2 0.5 and 1.0. Bronchoscopy, plain radiographs, and spiral computed tomographic (CT) scans were performed. Lung biopsies were obtained pre- and post-reperfusion. Ex vivo perfusion did not cause increased wet to dry ratio, or major abnormalities by microscopy but was associated with elevated tissue levels of conjugated dienes. The alveolar-arterial difference in partial pressure of oxygen (Pao2)/Fio2 ratio in the ex vivo circuit was generally higher than in the six donors. Ex vivo radiographs and CT scans were abnormal in all lungs, confirming unsuitability of these lungs for transplant. Ex vivo evaluation of human lungs is feasible and may be useful to evaluate transplant suitability of lungs retrieved after circulatory arrest from non-heart-beating donors.

Acute Pulmonary Embolism: Correlation of CT Pulmonary Artery Obstruction Index with Blood Gas Values

The purpose of our study was to investigate the relation between the pulmonary artery obstruction index assessed with helical CT and impairment in blood gases in patients with acute pulmonary embolism. Helical CT pulmonary angiography was performed in 78 patients who were suspected of having acute pulmonary embolism and selected as being free of underlying cardiopulmonary disease. Findings consistent with acute pulmonary embolism were observed in 34 patients. The severity was assessed by the pulmonary artery obstruction index, defined as Sigma (n x d), where n is the number of segmental arteries occluded and d is the degree of obstruction. Spearman's rank correlation coefficients were used to assess the correlation between the index of arterial obstruction and arterial partial pressure of oxygen (Pao(2)); alveolar-arterial difference in partial pressure of oxygen (Pao(2)-Pao(2)); arterial partial pressure of carbon dioxide (Paco(2)); and arterial oxygen saturation (Sao(2)). The statistical difference of the arterial blood gas values between the two groups of patients (those with and those without pulmonary embolism) was evaluated using the Mann-Whitney U test. Blood gases were comparatively evaluated below and above different index values (from 40% to 70%) and different Paco(2) values (25, 30, and 35 mm Hg) as possible indexes of embolism severity using the same test. The level of significance was set at 95% (p = 0.05). The values of Pao(2), Sao(2), and Paco(2) were significantly lower (p = 0.024, p = 0.0062, and p = 0.000075, respectively) and the values of Pao(2)-Pao(2) were significantly higher (p = 0.0169) in the pulmonary embolism group than in the no-pulmonary-embolism group. A significant correlation was observed between the obstruction index and Pao(2) (r = -0.33, p = 0.05), Paco(2) (r = -0.34, p = 0.05), Pao(2)-Pao(2) (r = 0.39, p = 0.02), and Sao(2) (r = -0.35, p = 0.04). Using cutoff values for the pulmonary artery obstruction index of 40%, 50%, 60%, and 70%, we observed that Paco(2) and Pao(2)-Pao(2) differed significantly between above and below the 40% (p = 0.018 and p = 0.03), 50% (p = 0.0087 and p = 0.029), and 60% (p = 0.005 and p = 0.003) cutoffs. Pao(2) differed significantly for the cutoff values of 60% (p = 0.03) and 70% (p = 0.004). The same was observed for Sao(2) at 60% (p = 0.05) and 70% (p = 0.03). Comparisons for Paco(2) showed that a value of 30 mm Hg significantly separates levels of the pulmonary artery obstruction index (p = 0.002), with 78% sensitivity and 82% specificity indicating a pulmonary artery obstruction index greater than 50%. In patients with acute pulmonary embolism but no other underlying cardiopulmonary disease, the severity of the pulmonary arterial tree obstruction assessed using the CT obstruction index is significantly correlated to the blood gas values. The strongest correlation was observed between the index and the Pao(2)-Pao(2). Furthermore, a Paco(2) value of 30 mm Hg or less is highly suggestive of an obstruction index of more than 50% of the arterial bed.

Hospital and 1-Year Survival of Patients Admitted to Intensive Care Units with Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Objective. —To describe outcomes and identify variables associated with hospital and 1-year survival for patients admitted to an intensive care unit (ICU) with an acute exacerbation of chronic obstructive pulmonary disease (COPD). Design. —Prospective, multicenter, inception cohort study. Setting. —Forty-two ICUs at 40 US hospitals. Patients. —A total of 362 admissions for COPD exacerbation selected from the Acute Physiology and Chronic Health Evaluation (APACHE) III database of 17440 ICU admissions. Measurements and Results. —Hospital mortality for the 362 admissions was 24%. For the 167 patients aged 65 years or older, mortality was 30% at hospital discharge, 41% at 90 days, 47% at 180 days, and 59% at 1 year. Median survival for all patients was 224 days, and median survival for the patients who died within 1 year was 30.5 days. On multiple regression analysis, variables associated with hospital mortality included age, severity of respiratory and nonrespiratory organ system dysfunction, and hospital length of stay before ICU admission. Development of nonrespiratory organ system dysfunction was the major predictor of hospital mortality (60% of total explanatory power) and 180-day outcomes (54% of explanatory power). Respiratory physiological variables (respiratory rate, serum pH, Paco2, Pao2, and alveolar-arterial difference in partial pressure of oxygen [Pao2—Pao2]) indicative of advanced dysfunction were more strongly associated with 180-day mortality rates (22% of explanatory power) than hospital death rates (4% of explanatory power). After controlling for severity of illness, mechanical ventilation at ICU admission was not associated with either hospital mortality or subsequent survival. Conclusions. —Patients with COPD admitted to an ICU for an acute exacerbation have a substantial hospital mortality (24%). For patients aged 65 years or older, mortality doubles in 1 year from 30% to 59%. Hospital and longer-term mortality is closely associated with development of nonrespiratory organ system dysfunction; severity of the underlying respiratory function substantially influences mortality following hospital discharge. The need for mechanical ventilation at ICU admission did not influence either short- or long-term outcomes. Physicians should be aware of these relationships when making treatment decisions or evaluating new therapies. (JAMA. 1995;274:1852-1857)

Effects of intramuscular or interpleural administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy

Abstract Objective To evaluate effects of interpleural or IM administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy. Design Experimental trial. Animals 18 healthy dogs. Procedure Dogs underwent median sternotomy and were randomly assigned to groups of 6 dogs each. Group-A dogs were given morphine (1.0 mg/kg of body weight) IM; group-B dogs were given 0.5% bupivacaine (1.5 mg/kg) interpleurally; and group-C dogs were given morphine (1.0 mg/kg) interpleurally. Heart rate; systolic, diastolic, and mean arterial pressures; rectal temperature; pain score; and arterial blood gas partial pressures were measured and pulmonary function testing was performed immediately after extubation (time 0) and up to 48 hours later. Serum cortisol and morphine concentrations were measured at time 0 and up to 12 hours after surgery. Results There was a significant decrease in pH, Pao2, mean oxygen saturation of hemoglobin, and dynamic compliance; and a significant increase in Paco2. alveolar-arterial difference in partial pressure of oxygen, pulmonary resistance, and work of breathing for dogs in all groups after surgery. Serum cortisol concentrations were significantly increased, compared with preoperative values, in all dogs. Serum cortisol concentrations were significantly higher in group-B dogs between 3 and 5 hours after surgery, compared with group-A dogs. Conclusions Median sternotomy was associated with significant alterations in pulmonary function. Effects of interpleural administration of bupivacaine and morphine were similar to effects of IM administration of morphine.(Am J Vet Res 1996;57:375-380)

Hospital and 1-Year Survival of Patients Admitted to Intensive Care Units With Acute Exacerbation of Chronic Obstructive Pulmonary Disease

To describe outcomes and identify variables associated with hospital and 1-year survival for patients admitted to an intensive care unit (ICU) with an acute exacerbation of chronic obstructive pulmonary disease (COPD). Prospective, multicenter, inception cohort study. Forty-two ICUs at 40 US hospitals. A total of 362 admissions for COPD exacerbation selected from the Acute Physiology and Chronic Health Evaluation (APACHE) III database of 17,440 ICU admissions. Hospital mortality for the 362 admissions was 24%. For the 167 patients aged 65 years or older, mortality was 30% at hospital discharge, 41% at 90 days, 47% at 180 days, and 59% at 1 year. Median survival for all patients was 224 days, and median survival for the patients who died within 1 year was 30.5 days. On multiple regression analysis, variables associated with hospital mortality included age, severity of respiratory and nonrespiratory organ system dysfunction, and hospital length of stay before ICU admission. Development of nonrespiratory organ system dysfunction was the major predictor of hospital mortality (60% of total explanatory power) and 180-day outcomes (54% of explanatory power). Respiratory physiological variables (respiratory rate, serum pH, PaCO2, PaO2, and alveolar-arterial difference in partial pressure of oxygen [PAO2-PaO2]) indicative of advanced dysfunction were more strongly associated with 180-day mortality rates (22% of explanatory power) than hospital death rates (4% of explanatory power). After controlling for severity of illness, mechanical ventilation at ICU admission was not associated with either hospital mortality or subsequent survival. Patients with COPD admitted to an ICU for an acute exacerbation have a substantial hospital mortality (24%). For patients aged 65 years or older, mortality doubles in 1 year from 30% to 59%. Hospital and longer-term mortality is closely associated with development of nonrespiratory organ system dysfunction; severity of the underlying respiratory function substantially influences mortality following hospital discharge. The need for mechanical ventilation at ICU admission did not influence either short- or long-term outcomes. Physicians should be aware of these relationships when making treatment decisions or evaluating new therapies.

Pulmonary gas exchange during orthotopic liver transplantation

The aim of this study was to evaluate the efficiency of pulmonary gas exchange during the course of liver transplantation. We studied 25 adult cirrhotic patients undergoing transplantation, performed with venovenous bypass. A significant increase in PaO2, and a significant decrease in physiological shunt and alveolar-arterial partial pressure difference were observed just before the start of venovenous bypass. These changes were probably caused by modifications in respiratory mechanics, such as an increase in functional residual capacity. There were no other respiratory changes during the anhepatic and post-anhepatic phases.

Inhaled nitric oxide in infants referred for extracorporeal membrane oxygenation: Dose response

To determine the role of inhaled nitric oxide (NO) in a population of critically ill hypoxic near-term infants and to determine the dose response to inhaled NO, we examined a consecutive group of 23 infants referred for neonatal extracorporeal membrane oxygenation (ECMO) who had an oxygen index of 20 or greater after treatment with bovine surfactant. Inhaled NO was administered in concentrations from 5 to 80 ppm in random order to 23 infants. Overall, 13 infants had a significant response (an improvement in arterial oxygen pressure > 10 mm Hg or arterial oxygen saturation > 10%) to the first administration of inhaled NO, and one infant had a late response. There was no significant difference in the response to inhaled NO as measured by changes in arterial oxygen pressure or in the alveolar-arterial difference in partial pressure of oxygen, for any of the doses from 5 to 80 ppm. Thirteen infants had echocardiographic evidence of persistent pulmonary hypertension; 11 of these infants responded, compared with 3 responders among the 10 infants without persistent pulmonary hypertension of the newborn ( p < 0.01). Overall, 11 infants required ECMO; there were two deaths in this group. Seven infants had congenital diaphragmatic hernia; five of those had a response to NO inhalation and four required ECMO. Our study demonstrates that there is no significant difference in response between low and high doses of inhaled NO and that this treatment may prevent the need for ECMO in some infants referred for this therapy, especially in infants with pulmonary hypertension. Prospective, controlled, randomized, and blinded trials of low doses of inhaled NO are needed to determine the clinical role of this potentially useful therapy. (J P EDIATR 1994;124:302-8)

Respiratory and inert gas exchange during high-frequency ventilation.

Pulmonary gas exchange during high-frequency low-tidal volume ventilation (HFV) (10 Hz, 4.8 ml/kg) was compared with conventional ventilation (CV) and an identical inspired fresh gas flow in pentobarbital-anesthetized dogs. Comparing respiratory and infused inert gas exchange (Wagner et al., J. Appl. Physiol. 36: 585--599, 1974) during HFV and CV, the efficiency of oxygenation was not different, but the Bohr physiological dead space ratio was greater on HFV (61.5 +/- 2.2% vs. 50.6 +/- 1.4%). However, the elimination of the most soluble inert gas (acetone) was markedly enhanced by HFV. The increased elimination of the soluble infused inert gases during HFV compared with CV may be related to the extensive intraregional gas mixing that allows the conducting airways to serve as a capacitance for the soluble inert gases. Comparing as exchange during HFV with three different density carrier gases (He, N2, and Ar), the efficiency of elimination of Co2 or the intravenously infused inert gases was greatest with He-O2. However, the alveolar-arterial partial pressure difference for O2 on He-O2 exceeded that on N2-O2 by 5.4 Torr during HFV. The finding agrees with similar observations during CV, suggesting that this aspect of gas exchange is not substantially altered by HFV.

The alveolar-arterial difference for O 2 and CO 2 in an infinite alveolus lung model

An infinite-alveolus model of the lung is developed with a continuous distribution of local alveolar ventilation and local perfusion. In this model we treat only linear distributions of these two variables. First approximations to the exact analytic expressions are derived for the alveolar-arterial partial pressure difference for both oxygen and carbon dioxide, that is, the A-a P O 2 and the A-a P CO 2 differences.