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Biomedical subjects

S M Scharf

Publications and source records attributed to S M Scharf.

At least 73 records · Page 4Linked to original sources
PubMed1991

Cardiovascular effects of airways obstruction.

Airways obstruction is usually associated with substantial decreases in inspiratory and mean intrathoracic pressure (ITP). The change in ITP is correlated with the degree of inspiratory fall in arterial pressure, pulsus paradoxus. The factors influencing the degree of pulsus include venous return, afterload effects on the left ventricle (LV), diastolic ventricular interdependence, lung volume, and circulatory reflexes. I have reviewed these factors and attempted to demonstrate that their relative importance changes under different circumstances. I have discussed the importance of measuring transmural pressures to assess ventricular performance, and pointed out some possible pitfalls in the use of esophageal or pleural pressure to estimate LV surface pressure. During normal and loaded inspiration, decreased LV preload, probably related to right ventricle (RV)-LV diastolic interdependence, appears to be the primary mechanism responsible for decreased stroke volume during inspiration. During Mueller maneuvers, and possibly with severe decreases in ITP. LV afterload may be more important. When lung volume increases, as with asthma, venous return from the lower body may be a more important determinant of pulsus paradoxus. Although previous predictions that decreased ITP would lead to increased myocardial O2 consumption were not borne out, coronary blood flow did increase with inspiratory loading. This appears to be due to a nonvagally mediated change in autonomic tone with loaded breathing. This and other reflex-mediated effects deserve more attention in future studies of stressed or abnormal inspiration. As a final point, pericardial tamponade probably leads to pulsus paradoxus by exaggerating normal diastolic right-left interactions.

Blood Pressure↗
PubMed1991

Effect of chronic resistive loading on inspiratory muscles in rats.

The development of animal models of respiratory muscle training would be useful in studying the physiological effects of training. Hence, we studied the effects of chronic resistive loading (CRL) for 5 wk on mass, composition, and mechanics of inspiratory muscles in laboratory rats. CRL was produced by means of a tracheal cannula (loaded animals) and results were compared with sham-operated controls. Acutely, upper airway obstruction led to a doubling of inspiratory pleural pressure excursion and 25% decrease in respiratory rate. We observed no changes in lung pressure-volume curves, nor in the geometry of the respiratory system in loaded compared with control animals. Muscle mass normalized for body mass increased in the diaphragm (DI) and the wet weight-to-dry weight ratio increased in the sternomastoid (SM) in loaded compared with control animals. Loaded animals demonstrated a decrease in ether extractable (fat) content of the DI and SM muscles but not the gastrocnemius. For the DI there was no change in length at which active tension was maximal (Lo), but there was an increase in maximum tension at lengths close to Lo in loaded compared with control rats. Endurance did not change, although twitch tensions remained higher in loaded compared with control rats. We conclude that 1) alteration of inspiratory muscle structure and function occurs in rats with CRL; 2) the DI and SM demonstrate different adaptive responses to CRL; and 3) although maximum tension increases, endurance does not.

Animals↗
PubMed1990

Screening for subclinical sleep-disordered breathing.

We evaluated self-administered questionnaires and short sleep studies in screening for sleep-disordered breathing (SDB) in 40 hypertensive men ages 36-66 unselected for symptoms. Each subject completed a questionnaire including questions on sleep-related symptoms and underwent overnight polysomnography in which we evaluated the apnea-hypopnea index (AHI) and the percentage of time during which arterial O2 saturation was less than 90% (T90). The first 90 min of overnight study was evaluated separately, and 10 subjects with an AHI greater than or equal to 10 also underwent late afternoon nap study. By overnight polysomnography, 48% of the cohort had an AHI greater than or equal to 10, and 35% had a T90 greater than or equal to 10%. Using linear regression, we found no features of the symptom questionnaire that strongly predicted AHI. Only self-reported snoring and baseline arterial Po2 significantly predicted T90. The AHI and T90 were not significantly correlated. Considering an AHI greater than or equal to 10 in the overnight study as "abnormal" and an AHI greater than or equal to 10 on the short study as a "positive" test, the specificity of the AHI in the first 90 min was 100% (21/21), and the sensitivity was 42% (8/19). The sensitivity of the nap study was 60% (6/10). We conclude that in a cohort unselected for symptoms, the ability of self-administered questionnaires to predict SDB was low; short studies were only moderately sensitive for detecting an AHI greater than or equal to 10, and the AHI was not a major determinant of nocturnal desaturation.

Adult↗
PubMed1989

Intrathoracic pressures and left ventricular configuration with respiratory maneuvers.

In 12 dogs, we examined the correspondence between esophageal (Pes) and pericardial pressures over the anterior, lateral, and inferior left ventricular (LV) surfaces. Pleural pressure was decreased by spontaneous inspiration, Mueller maneuver, and phrenic stimulation and increased by intermittent positive pressure ventilation (IPPV) and positive end-expiratory pressure (PEEP). To separate effects due to blood flow, we analyzed beating and nonbeating hearts. In beating hearts, there were no significant differences between changes in Pes and pericardial pressures. In arrested hearts, increasing LV pressure by 8 Torr increased pericardial pressures by only 3.6 Torr. With IPPV and PEEP, increases in Pes and pericardial pressures were equal in live hearts and in low-volume arrested hearts (LV pressure = 4 Torr). In high-volume arrested hearts (LV pressure = 12 Torr), the increase in pericardial pressure over the anterior LV surface was less than Pes, whereas that over the lateral and inferior LV surfaces was the same as Pes. At high LV volume, in arrested hearts pericardial pressures decreased less than Pes during negative pressure maneuvers. In another six dogs, external LV configuration and volume were measured. In beating hearts during spontaneous inspiration, Mueller maneuver, and phrenic stimulation (endotracheal tube open), septal-lateral dimension and LV volume decreased by approximately 3% (P less than 0.05). This was also true for PEEP. In arrested hearts, septal-lateral dimension and LV volume decreased only with PEEP. We conclude that 1) the relationship between Pes and pericardial pressures is complex and depends on LV volume, local pericardial compliance, and the means by which Pes is changed, 2) changes in measured pericardial pressures did not completely explain changes in LV configuration, and 3) during different respiratory maneuvers, different forces account for the same observed changes in LV volume and configuration.

Animals↗
PubMed1989

Diaphragm metabolism during supramaximal phrenic nerve stimulation.

The metabolic changes accompanying diaphragm fatigue caused by supramaximal stimulation of the phrenic nerves are incompletely described. In particular, we wished to determine whether the occurrence of anaerobic metabolism correlated with fatigue as defined by decline in force generation. In 10 anesthetized mechanically ventilated mongrel dogs we measured arterial pressure, transdiaphragmatic pressure (Pdi), phrenic arterial flow (Qdi-Doppler flow probe), arterial and phrenic venous blood gases, and lactate levels. From these we derived indexes of diaphragm O2 consumption (VO2) and lactate production. Bilateral phrenic nerve pacing was carried out (50 Hz, duty cycle 0.4, 24 contractions/min) for two 15-min pacing periods separated by a 45-min rest period. Over each pacing period Pdi decreased from approximately 16 to approximately 10 cmH2O (P less than 0.01, no significant difference between periods). Initially, during pacing, Qdi and VO2 each increased fivefold over prepacing base line. Qdi remained elevated at this level whereas VO2 decreased over the pacing period by approximately 25%. Hence, the change in VO2 over the pacing period was due primarily to changes in O2 extraction. During the first pacing period lactate production was observed early and declined throughout the pacing period. No lactate production was observed during the second pacing period, although Pdi, VO2, and Qdi responses were the same for both pacing periods. Phrenic venous PO2 remained greater than 30 Torr throughout both pacing periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Correlation of left phrenic arterial flow with regional diaphragmatic blood flow.

Previous work has assumed that left phrenic arterial blood flow (Qpa) reflects diaphragmatic blood flow. We have tested this assumption in four anesthetized mechanically ventilated dogs by measuring Qpa with a Doppler flow probe and regional diaphragmatic blood flow with radiolabeled microspheres. Flows were examined during control 1 (diaphragm at rest), pacing (phrenic pacing: rate 20/min, duty cycle 0.33), control 2, hypotension (rest with mean arterial pressure reduced by 45% of the control 1 value), and hypotension and pacing. As a percent of the control 1 value, Qpa was 511 +/- 107% during pacing, 139 +/- 12% during control 2, 40 +/- 13% during hypotension, and finally 347 +/- 31% during hypotension and pacing. Similarly, percent left hemidiaphragmatic blood flow (Qlh) was 362 +/- 91% during pacing, 91 +/- 10% during control 2, 14 +/- 2% during hypotension, and finally 213 +/- 50% during hypotension and pacing. The changes in flow to the left costal and crural diaphragm were similar to those recorded for Qlh. We conclude that Qpa correlates with total and regional diaphragmatic blood flow (r = 0.77-0.81, P less than 0.001) under conditions of supramaximal phrenic nerve stimulation in which the metabolic demands of the region perfused by the phrenic artery are presumed to be similar to the metabolic demands of the rest of the diaphragm.

Animals↗
PubMed1987

Effects of the Mueller maneuver on global and regional left ventricular function in angina pectoris with or without previous myocardial infarction.

In patients with coronary artery disease, left ventricular (LV) regional wall akinesia can develop during the Mueller maneuver. The present study determines if the presence of myocardial ischemic disease with no infarction is a sufficient condition for this to occur, or if the presence of prior acute myocardial infarction (MI) is necessary. In men, first-pass radionuclide ventriculography was performed in the 30 degree left anterior oblique supine position to measure LV ejection fraction, end-diastolic and end-systolic volumes and heart rate, and to obtain an image of the LV cavitary perimeter. This procedure was performed in 4 subject groups: 13 normal volunteers, 25 patients with coronary artery disease but no prior MI, 13 patients with coronary artery disease and prior nontransmural MI, and 36 patients with coronary artery disease and prior transmural MI. All patients had angina and underwent routine contrast coronary angiography; 60 also underwent contrast coronary angiography; 60 also underwent contrast LV angiography. Ejection fraction decreased during the Mueller maneuver in each of all the coronary artery disease groups (p less than 0.01), but not in the normal subjects. Heart rate increased in groups 1, 2 and 4 (p less than 0.01), and end-diastolic volume decreased in all 4 groups (p less than 0.01), whereas end-systolic volume did not change. Only in group 4 did regional wall akinesia develop (17 patients) during the Mueller maneuver. Among patients who had akinesia during the Mueller maneuver and also underwent routine contrast ventriculography, half of the akinetic segments were not seen on routine contrast study, but were seen only on radionuclide ventriculography during the Mueller maneuver.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1987

Mueller maneuver and LV function in coronary artery disease.

Decreasing pleural pressure impedes the ejection of blood from the left ventricle (LV), may lead to decreased LV compliance because of interdependence effects and leads to increased transmural LV systolic and diastolic pressure. Previous work from this laboratory has shown that patients with coronary artery disease (CAD) often develop akinetic segments of the LV wall during the Mueller maneuver. In the presence of increased LV transmural pressure regional akinesis could be caused either by the development of regional ischemia or by mechanical inhibition of motion of an area of nonfunctional myocardium as would be caused by previous myocardial infarction (MI). The present study was designed to distinguish between these two mechanisms by determining if the presence of CAD alone is sufficient to lead to regional akinesis or if prior MI is necessary. We used first pass radionuclide ventriculography (RVG) in the 30 degrees LAD supine position to measure LV ejection fraction (EF), end-diastolic (EDV) and end-systolic (ESV) volumes, heart rate and to assess regional wall motion during the Mueller maneuver. This was done in four groups of subjects: 13 normal subjects, 25 patients with CAD but no prior MI, 13 patients with prior nontransmural MI and 36 patients with prior transmural MI. All subjects had angina pectoris and underwent contrast coronary arteriography. Most also underwent routine contrast left ventriculography as well. There were no significant differences among the three patient groups as regards medications, extent and severity of CAD, and response to routine exercise tolerance testing. EF decreased significantly in the three patient groups (4%-9%, p less than 0.01) but not in the normals during the Mueller maneuver. Heart rate increased (5-10 bpm, p less than 0.05) in the normals and in patient groups 2 and 4. EDV decrease in all four subject groups (8%-10%, p less than 0.01), while ESV remained unchanged. Akinesis of the LV wall developed during the Mueller maneuver only in one group-2 patient, but did so in 17/36 patients with prior transmural MI (group 4, p less than 0.001). One-half of the akinetic LV wall segments seen during the Mueller maneuver on RVG were not seen on routine contrast ventriculography. We tested the effects of posture (supine versus upright) on the response to the Mueller maneuver in six normal subjects and found no changes in the response of EDV and ESV to the Mueller maneuver.(ABSTRACT TRUNCATED AT 400 WORDS)

Coronary Disease↗
PubMed1987

Cardiovascular performance during bronchospasm in dogs.

In 8 anesthetized mongrel dogs, we studied the effects of carbachol-induced bronchoconstriction (BC) on the cardiovascular system. Inhalation of carbachol in an amount sufficient to produce at least a 50% decrease in lung conductance (GL) did not lead to significant changes in cardiac output, mean transmural left atrial (Pla) or right atrial pressure, end-diastolic left ventricular septal-lateral dimension, left ventricular apex to base dimension, or in end-diastolic right ventricular septal to lateral dimension during expiration. Mean transmural pulmonary arterial pressure rose and mean transmural aortic pressure (Pao) fell during BC. During inspiration, there were significant increases in transmural left atrial pressure, Pla, associated with decreases in end-diastolic left ventricular septal-lateral and apex-base dimensions. End-diastolic right ventricular septal-lateral dimension increased during inspiration. Beat-to-beat aortic flow (Qao) decreased during inspiration, while pulmonary arterial flow increased. There were no changes in transmural Pao during inspiration measured at the nadir of aortic flow. During BC, these changes were exaggerated, but remained qualitatively the same. The magnitude of the inspiratory decrease in pleural pressure (Ppl) was shown to be linearly related to the magnitude of the change in GL, and the magnitude of the inspiratory decrease in Pao and Qao (pulsus paradoxus) was shown to be linearly related to the magnitude of the inspiratory swing in Ppl. Although vagotomy significantly altered the pattern of respiration such that tidal volume increased and respiratory rate decreased, it did not substantially alter the responses of the cardiovascular system to breathing during BC. We conclude: the inspiratory decrease in Pao and Qao (pulsus paradoxus) is associated with a decrease in left ventricular end-diastolic filling, and a stiffening of the left ventricle; these changes are exaggerated during BC as a result of the exaggerated inspiratory swings in Ppl; the effects on left ventricular dynamics are mediated only in part through increases in right ventricular end-diastolic filling operating through the mechanism of ventricular interdependence; changes in left ventricular afterload appear to play little role in determining the responses seen.

Airway Resistance↗
PubMed1986

Effect of phrenic nerve stimulation on neural transmission and diaphragmatic force generation in the dog.

The effect of supramaximal bilateral phrenic nerve stimulation on neural transmission and diaphragmatic force generation was studied in anesthetized dogs. Different combinations of duty cycle and stimulation frequency were examined during intermittent stimulation (pacing) for 15 min. The effect of different stimulation frequencies was also examined during continuous stimulation for 60 sec. Force declined more with increasing stimulation frequency and duty cycle with intermittent stimulation, and with increasing stimulation frequency with continuous stimulation. Neural transmission decreased with increasing stimulation frequencies. The changes were always greater with continuous than with intermittent stimulation. We found no unique relationship between changes in neural transmission and changes in force generation, suggesting that if neural transmission failure is causally responsible for fatigue, it does so by a very complex mechanism.

Action Potentials↗
PubMed1986

Pulmonary function screening and monitoring in occupational health.

Lung function testing among occupationally exposed workers has demonstrated its usefulness in risk evaluation and, once risks are identified, in medical surveillance. Its usefulness for screening and biological monitoring for effects of exposure is not yet established; in part, this is due to some failure to understand the requirements for screening and for monitoring, and in part, it is due to some unresolved questions as to procedures and their interpretation. The use of screening in occupational groups in general and those exposed to inhalational risks is evaluated. The current recommendation is that priority for screening be given to risk factor reduction, including smoking cessation. Problems associated with screening relate to procedures, equipment, and interpretation of data. An agenda is proposed for an international effort to determine principles for epidemiological use of lung function tests for prevention of occupational pulmonary disease risks.

Adult↗
PubMed1986

Diaphragmatic blood flow in the dog.

In anesthetized mongrel dogs we measured the blood flow in the left phrenic artery (Qdi), using an electromagnetic flow probe, before and during supramaximal phrenic nerve stimulation (pacing). This was done at constant respiratory rate (24/min) but at three different stimulation frequencies at a duty cycle of 0.4 (20, 50, and 100 Hz) and at three different duty cycles at a stimulation frequency of 50 Hz (duty cycle = 0.2, 0.4, and 0.8). Qdi was unchanged during diaphragm contraction until transdiaphragmatic pressure (Pdi) was greater than approximately 11 cmH2O, whereafter it began to decrease, reaching zero at Pdi approximately 20 cmH2O. Thus, when Pdi was greater than 21 cmH2O, all flow occurred during relaxation. Qdi averaged over the entire respiratory cycle (Qt) was less at duty cycle = 0.8 than under the other conditions. This was because of decreasing length of relaxation phase rather than a difference of relaxation phase flow (Qr), which was maximal during all conditions of phrenic stimulation. During pacing-induced fatigue, Qt actually rose slightly as Pdi fell. This was due to an increase in contraction phase flow while Qr remained constant. The relationship between Qt and tension-time index was not unique but varied according to the different combinations of duty cycle and stimulus frequency.

Animals↗
PubMed1986

Blood flow to the canine diaphragm during hemorrhagic shock.

Previous studies have shown impairment of diaphragm function during shock. It is possible that the mechanism for this is decreased diaphragm perfusion, which leads to decreased function because of limitation of oxygen transport. In order to examine the degree to which oxygen transport is limited during shock, we measured the changes in blood flow to and oxygen consumption of the diaphragm during controlled hemorrhage. Blood flow through the left phrenic artery (Qdi) was measured with an electromagnetic flow probe as systemic arterial pressure (Pa) was decreased. The Pa-Qdi relationship was found to be linear with slope of approximately 0.145 ml/torr/min, and extrapolated pressure at zero flow of approximately 40 torr in normal control subjects. Inspiratory loading and infusion of isoproterenol led to a parallel shift in the Pa-Qdi curve such that there was a decrease in the extrapolated pressure at zero flow to 9 to 13 torr. Infusion of dopamine led to a parallel shift of the Pa-Qdi curve such that there was an increase in the extrapolated pressure at zero flow from approximately 34 to approximately 45 torr. In the normal control subjects, there was a decrease in oxygen consumption associated with the decrease in Qdi, but this was not true for either loading or isoproterenol. We conclude that during hypotension, blood flow to the diaphragm decreases. However, the diaphragm retains the ability to increase its blood flow in response to metabolic or pharmacologic stimuli. This is done primarily by a parallel shift in the pressure-flow relationship, which may represent a change in the critical closing pressure of the phrenic vasculature.

Animals↗
PubMed1985

Bronchial challenge with room temperature isocapnic hyperventilation. A comparison with histamine challenge.

We evaluated isocapnic hyperventilation with room temperature gas (IHV) as a test of bronchial hyperreactivity and compared it with histamine challenge (HC) in three groups of subjects: normal subjects, known mild asthmatic patients, and patients referred to the pulmonary clinic for a chief complaint of dyspnea. Physical examination at the time of evaluation was negative in all subjects. When the criterion for a positive reaction to IHV was a decrease in FEV1 of 10 percent or greater, and the criterion for a positive reaction to HC was a PD20 (concentration of inhaled histamine necessary to decrease FEV1 by at least 20 percent) of less than 10 mg/ml, the specificity of both tests was 100 percent. The sensitivity of both tests as evaluated from the known asthmatic patients was also 100 percent. Among the dyspneic patients, eight of 30 reacted to both IHV and HC, two of 30 reacted to HC alone, and eight of 30 reacted to IHV alone. It was concluded that IHV compares favorably with HC as a test of bronchial hyperreactivity, patients with clinical histories highly suggestive for asthma might not need to undergo bronchial challenge testing, and neither HC nor IHV when used alone is able to identify all of the hyperreactive patients.

Adolescent↗
PubMed1985

Fiberoptic bronchoscopy in patients with hemoptysis and nonlocalizing chest roentgenograms.

We reviewed retrospectively the records of 45 patients undergoing fiberoptic bronchoscopy for hemoptysis in whom chest roentgenograms either were normal or showed only nonlocalizing findings. Follow-up was available for up to three years. In none of the patients was evidence of malignant neoplasms found either at the time of the initial evaluation or at the time of follow-up. This was true for all age groups and for smokers as well as nonsmokers. We conclude that routine fiberoptic bronchoscopy for hemoptysis is not necessarily indicated in patients like ours. Indications for this procedure in this type of case should be carefully weighed.

Adult↗
PubMed1984

Residual small airways lesions after kerosene pneumonitis in early childhood.

To assess residual lung damage after a single insult early in life, we studied 14 asymptomatic children, 10 years after an episode of kerosene pneumonitis. Immediately after kerosene ingestion all patients developed pulmonary symptoms. Eight had abnormal chest radiographs (group 1) whereas in six there were no radiographical changes (group 2). The average age at follow-up was 11.4 (range: 9.4-13.2). Lung volumes, expiratory flow-rates and their density dependence were measured and compared to an age, sex, and a height-matched control group. The volume of isoflow (Viso V) was significantly higher in patients in group 1 (27.75% +/- 6.7) when compared to group 2 (5.48% +/- 3.56) or controls (5.63% +/- 2.31) (P less than 0.02). The mean delta V max 50 was 13.5% +/- 3 for group 1, and 27.9% +/- 4.11 for group 2 (P less than 0.005). Airway reactivity assessed by an exercise test was normal in all children. Four of the eight patients from group 1 still had abnormal chest radiographs 10 years after kerosene pneumonitis. Thus, subclinical, prolonged small airway abnormalities after kerosene pneumonitis seem to be related to the severity of the acute insult.

Adolescent↗