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Biomedical subjects

D R Dantzker

Publications and source records attributed to D R Dantzker.

At least 55 records · Page 3Linked to original sources
PubMed1985

Magnitude and implications of spontaneous hemodynamic variability in primary pulmonary hypertension.

The pulmonary artery (PA) pressure and pulmonary resistance at rest have been noted to vary spontaneously in patients with primary pulmonary hypertension. To evaluate this variation, in 12 patients (8 women, 4 men, aged 43 +/- 13 years), hourly measurements were made for 6 consecutive hours of heart rate, systemic and PA pressures, cardiac output, systemic and pulmonary resistance. After these baseline measurements the patients were tested with hydralazine and nifedipine therapy. Spontaneous variability in pulmonary pressures and resistances occurred in each patient, with the amount of variation (coefficient of variation) in PA pressure averaging 8% and in total pulmonary resistance 13% over the 6 hours. The patients with the most variability in mean PA pressure also had the most variability in cardiac output (r = 0.69, p = 0.02). Variability also correlated with the severity of the disease, as the patients with the highest total pulmonary resistances also had the most variation for that factor (r = 0.91, p less than 0.01). The amount of variability did not correlate, however, with the acute response to either hydralazine or nifedipine administration. Based on the average coefficients of variation in these 12 patients, estimates were obtained of the percent change needed for an observed change to be attributed to a drug effect with 95% confidence. From these estimates, it was projected that for a single patient, a mean change in pulmonary resistance of 36% or a mean change in PA pressure of 22% would be required in order to attribute the changes to a drug effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Comparison of canine cardiovascular response to inhaled and intraperitoneally infused CO.

We compared the hemodynamic and blood gas data from anesthetized dogs given 0.15% carbon monoxide (CO) to breathe (INH group) and from dogs injected with 100% CO intraperitoneally while breathing room air (ITP group). The animals were observed for a period of 150 min after reaching a level of 50% carboxyhemoglobin (HbCO). The time required to reach this level was similar for both groups, i.e., 102 +/- 54 and 90 +/- 21 min for the ITP and INH groups, respectively. The average HbCO% for the duration of the experiment was 58.3 +/- 2.4 and 62.9 +/- 1.5% for the ITP and INH groups, respectively. All the animals survived in each group. There was no significant difference in their hemodynamic response to CO, except for a higher mean systemic blood pressure in the INH group. This difference was also present during the base-line measurements, suggesting that it was not related to the effects of CO. Following the 150-min comparison period, we attempted to precipitate a terminal cardiovascular crisis by increasing the amount of CO given. The animals in the ITP group lived indefinitely as the result of a "plateau" effect in the level of HbCO%. The measured HbCO% level did not rise above 70% regardless of the amount of CO injected into the peritoneal space. Those in the inhalation group died with an average HbCO% of 80.0 +/- 3.5%. It is concluded that the toxic effect of CO is the result of impaired O2 delivery to the peripheral tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Pulmonary gas exchange and exercise performance in pulmonary hypertension.

Patients with pulmonary hypertension have disordered pulmonary gas exchange and impaired exercise tolerance. The hypoxemia is due to mild ventilation-perfusion (VA/Q) inequality exaggerated by the presence of a low mixed venous PO2 (PvO2) and is accentuated during exercise due to a further fall in PvO2. This in turn may be worsened by vasodilators which increase the degree of VA/Q inequality. Decreased exercise tolerance is due predominantly to cardiac limitation, and thus an improvement in cardiac function subsequent to successful vasodilation can be assessed by improved exercise performance.

Humans↗
PubMed1985

Evidence for adenosine triphosphate degradation in critically-ill patients.

Alterations of cellular energy metabolism may provide important markers during the clinical course of critically ill patients. To determine whether adenosine triphosphate (ATP) degradation occurs in critically ill patients, we measured levels of adenosine, inosine, hypoxanthine, and xanthine in 18 patients and seven control subjects. The mean concentration of hypoxanthine (3.8 microM) in the critically ill patients was elevated (p less than 0.01) compared to that of our control population (0.1 microM). A subgroup of seven critically ill patients had levels of hypoxanthine, xanthine, or inosine higher than those of any member of the control group. This subgroup was characterized by a lower systolic blood pressure, an increased requirement for vasopressors, and a markedly decreased survival rate when compared to the other critically ill patients. Arterial and mixed venous blood gas values were not helpful in predicting survival and did not correlate with levels of ATP degradation products. In two patients who showed subsequent clinical improvement, the initially elevated levels of hypoxanthine and xanthine returned to normal. This study indicates that critically ill patients have elevated levels of ATP degradation products. These increased levels may indicate cellular hypoxia.

Adenosine↗
PubMed1984

Adequacy of tissue oxygenation in intact dog intestine.

Changes in O2 consumption, O2 extraction, and intramural pH, resulting from a decreasing O2 delivery, were studied in the intact dog intestine. The O2 delivery was decreased by ischemia, hypoxia, and combined hypoxia-ischemia. A noninvasive approach for determining intramural pH based on the principle of tonometry was used. There was a strong correlation between the changes in intramural pH and intestinal O2 consumption as O2 delivery was decreased. Intramural pH and O2 consumption were initially maintained in the face of decreasing O2 delivery, but after a critical point they decreased. This critical point was 60.3 +/- 1.6% of base-line O2 delivery in the ischemic group and 51.3 +/- 2.7% of base line in the hypoxic-ischemic group. Despite a decrease to 36.0 +/- 5.6% of base-line O2 delivery, the intramural pH and O2 consumption did not decrease in the hypoxic group. O2 extraction increased with decreasing O2 delivery but did not plateau, indicating no diffusion limitation. The data suggest that blood flow is the major factor limiting intestinal O2 consumption. It is concluded that the noninvasive measure of intramural pH is a good marker of the adequacy of tissue oxygenation in canine intestine.

Animals↗
PubMed1984

Time domain analysis of diaphragmatic electromyogram during fatigue in men.

Diaphragmatic fatigue has been correlated with a change in the electromyogram recorded from the diaphragm (EMGdi), which suggests that the electromyogram is a potential clinical tool to detect respiratory muscle fatigue. Changes in the EMGdi have previously been quantified by using the power spectral parameters high-low ratio or mean frequency. In this study, we developed an autoregressive model of the EMG in an attempt to improve the analysis of the EMGdi. This model was tested on recordings of the EMGdi that were obtained from an esophageal electrode in five normal subjects breathing to fatigue through an inspiratory resistor. The data obtained from the autoregressive model were directly compared with data from the high-low ratio and mean frequency techniques. The autoregressive model showed an excellent correlation with mean frequency. Both techniques were superior to the high-low ratio measurement. Because the autoregressive model requires much less computation than mean frequency and can be easily implemented in real time on a minicomputer, we propose this as a preferable approach.

Adult↗
PubMed1984

Pulmonary gas exchange during exercise in patients with chronic obliterative pulmonary hypertension.

The effect of exercise on pulmonary gas exchange was investigated in 7 patients with pulmonary hypertension resulting from primary pulmonary hypertension or recurrent pulmonary emboli. During supine bicycle exercise averaging 2.4 times baseline O2 consumption there was a significant fall in the arterial PO2 (64 +/- 1.1 to 56 +/- 5.4) and widening of the alveolar-arterial gradient for O2 (50 +/- 4.6 to 62 +/- 5.5). Measurement of the distribution of ventilation-perfusion (VA/Q) ratios by the multiple inert gas technique demonstrated no increase in VA/Q inequality. The increased hypoxemia was due to the fall in the mixed venous PO2 and its impact on the end-capillary blood of the shunt and low VA/Q units present at both rest and exercise. A concomitant shift in the mean VA/Q ratio for the normal lung units mitigated but could not eliminate the fall in the arterial PO2. We conclude that the increased hypoxemia seen during exercise in these patients is due to the widened arterial-venous O2 difference expected with exercise and its effect on the mild VA/Q inequality characteristic of this disorder.

Adult↗
PubMed1984

Differentiation of patients with primary and thromboembolic pulmonary hypertension.

Twenty-five consecutive patients with obliterative pulmonary hypertension were studied. Primary pulmonary hypertension (17 patients) or chronic thromboembolic pulmonary hypertension (eight patients) was diagnosed by pulmonary angiography or autopsy. Clinical symptoms, physical findings, chest roentgenograms, electrocardiograms, and pulmonary function studies did not differentiate the patients with primary pulmonary hypertension (PPH) from those with chronic thromboembolic pulmonary hypertension (TPH). All eight patients with TPH had a lung scan interpreted as high probability for pulmonary emboli while all 17 patients with PPH had a lung scan interpreted as normal or low probability for emboli. While there was close clinical similarity between patients with PPH and TPH, the presence of a normal or low probability lung scan excluded the diagnosis of TPH.

Adult↗
PubMed1984

Gas exchange alterations following pulmonary thromboembolism.

This article reviews the many factors that may be involved in the development of abnormal gas exchange following a pulmonary thromboembolic event. Both pulmonary and nonpulmonary factors are examined. In addition, the diagnostic utility of obtaining arterial blood gases, dead space, and expired carbon dioxide will be examined.

Animals↗
PubMed1983

Respiratory failure, mechanisms of abnormal gas exchange, and oxygen delivery.

Patients with respiratory failure may have abnormal gas exchange based on a number of mechanisms. Each of these mechanisms may indicate a different underlying pathology and thus suggest different therapeutic interventions. In addition, the ability to monitor changes in physiologic function can be complicated but is achievable when proper protocols are followed. It should be clear that an adequate understanding of the underlying physiology is crucial to the successful management of these very difficult patients.

Humans↗
PubMed1983

The mechanisms of abnormal gas exchange in acute massive pulmonary embolism.

Hypoxemia usually accompanies acute pulmonary embolism in humans, but its mechanism remains poorly understood. We studied 2 patients with acute, massive pulmonary embolism (APE) documented by pulmonary angiography. Both patients had a markedly increased alveolar-arterial oxygen difference (AaPO2). The technique of multiple inert gas elimination was used to determine the distribution of ventilation-perfusion ratios (VA/Q). An increase in VA/Q inequality was found in both patients, but this increased inequality was caused entirely by an increase in the ventilation of lung units with high VA/Q ratio. No blood flow was found perfusing lung units with a VA/Q ratio of less than 1.0. Both patients, however, had a large amount of blood flow (20 and 39% of the cardiac output) perfusing unventilated lung units (shunt), and the percent of minute ventilation to unperfused lung units as well as the VD/VT determined from the Bohr equation were increased. We conclude that in these 2 patients with APE, VA/Q inequality did not play a major role in their hypoxemia and that the widened AaPO2 is explained by the large shunts that were found.

Acute Disease↗
PubMed1983

The influence of cardiovascular function on gas exchange.

Alterations in cardiovascular function may play a major role in determining pulmonary gas exchange and thus significantly influence the gas composition of the arterial blood. The influence of the cardiovascular system may be exerted through changes in the PvO2 or by directly altering the distribution of ventilation and blood flow in the lung. Although this relationship is difficult to clinically assess, it must always be considered when interpreting changes in the arterial blood gases of patients with cardiopulmonary dysfunction.

Animals↗
PubMed1982

Gas exchange at rest and during exercise in adults with cystic fibrosis.

The abnormalities of gas exchange at rest and during mild exercise were characterized in 6 adults with cystic fibrosis. All patients were hypoxemic at rest with a venous admixture ranging from 9.8 to 39.9%. Using the technique of multiple inert gas elimination we demonstrated that all 6 patients had significant intrapulmonary shunt and that this accounted for most of the venous admixture in three patients. In the remaining three patients there was, in addition, significant perfusion to lung units with low ventilation-perfusion ratios (VA/Q). The abnormalities of VA/Q adequately accounted for the measured arterial blood gases and no diffusion impairment for oxygen was noted. During exercise there was an improvement in the efficiency of gas exchange, but there were only minimal changes in the arterial PO2. This resulted from a widened arteriovenous O2 difference and in 2 patients an increase in shunt. The consistent presence of shunt and variability of the pattern of the VA/Q distributions differ from previously described studies in other patients with chronic airway obstruction.

Adolescent↗
PubMed1982

Gas exchange alterations associated with weaning from mechanical ventilation following coronary artery bypass grafting.

This study was done to clarify the effects of positive-pressure mechanical ventilation on gas exchange in the lungs of conscious patients. Nine hemodynamically stable patients were studied following coronary artery bypass grafting at the time they were weaned from mechanical ventilation. The adequacy of gas exchange was assessed by traditional measurements as well as the multiple inert gas technique used to measure the ventilation-perfusion (VA/Q) distribution. During mechanical ventilation, gas exchange was characterized by a variable degree of VA/Q inequality as well as a substantial shunt ranging from 11.9 to 27.7 percent. Following removal from mechanical ventilation, there was a decrease in the mean VA/Q subsequent to a decrease in the minute ventilation. However, there was no significant change in the level of shunt or in the amount of VA/Q inequality.

Aged↗