PubMed Health⌕ Search

Biomedical subjects

E R Greene

Publications and source records attributed to E R Greene.

At least 19 recordsLinked to original sources
PubMed1998

Arterial oxygen saturation for prediction of acute mountain sickness.

BACKGROUND: Acute mountain sickness (AMS) is a usually self-limiting syndrome encompassing headache, nausea and dizziness. AMS is seen in those that go from low to high altitudes too quickly, without allowing sufficient time to acclimatize. At present, susceptibility to AMS cannot be predicted. One feature of AMS noted in some studies is impaired gas exchange. If impaired gas exchange presages AMS then those individuals with exaggerated hypoxemia at high altitude may be more likely to develop AMS. If true, then monitoring of arterial oxygen saturation (SaO2%) may differentiate AMS-resistant individuals from those with impending AMS. METHODS: To test this hypothesis, we measured SaO2% and AMS symptom scores in 102 healthy asymptomatic climbers at 4200 m on Denali (Mt. McKinley) prior to their further ascent toward the summit at 6194 m, and on their return from higher altitudes to 4200 m. RESULTS: The results show that exaggerated hypoxemia in asymptomatic climbers prior to further ascent correlates with subsequent AMS (r = -0.48, p < 0.001). Criteria are presented for identification of 80-100% of those climbers who later become ill with AMS. CONCLUSION: We conclude that resting arterial hypoxemia is related to later development of clinical AMS, and can exclude the occurrence and caution those at risk for development of subsequent AMS. Likely mechanisms are hypoventilation relative to normally acclimatizing individuals and/or abnormalities of gas exchange. Thus, non-invasive oximetry provides a simple, specific indicator of inadequate acclimatization to high altitudes and impending AMS.

Acclimatization↗
PubMed1997

Temporal inhomogeneity in brachial artery blood flow during forearm exercise.

The purpose of this study was to measure the influences of muscle contraction and exercise intensity on brachial artery blood flow during incremental forearm wrist flexion exercise to fatigue. Twelve subjects performed incremental forearm exercise (increments of 0.1 W every 5 min) with their nondominant arms. Doppler waveforms and two-dimensional images of the brachial artery were recorded during the last 2 min of each stage. Exercise intensities were expressed as a percent of the maximal workload achieved (%WLmax). Blood flow was calculated during each of the concentric (CP), eccentric (EP), and recovery phases (RP) of the contraction cycle. Blood flow during the CP of the contraction did not increase above resting values (25.0 +/- 10.5 mL.min-1) at any intensity (100%WLmax = 21.6 +/- 6.5 mL.min-1). Conversely, blood flow during the EP and RP increased from 25.6 +/- 3.0 to 169.1 +/- 12.8 (P < 0.05), and from 24.7 +/- 3.1 to 137.9 +/- 19.5 mL.min-1 (P < 0.05), respectively from rest to maximal exercise. Time averaged blood flow increased linearly from rest to maximal exercise (75.3 +/- 26.3 to 334.6 +/- 141.6 mL.min-1, P < 0.05). Thus, a significant impairment in blood flow occurs with concentric contractions during forearm dynamic exercise. The implications of a temporal disparity in blood flow to oxygen delivery and skeletal metabolism during exercise are discussed.

Adult↗
PubMed1995

Central vascular flow patterns in the alligator Alligator mississipiensis.

Many different flow patterns have been described through the central circulation of crocodilian reptiles. We tested the hypothesis that the vagus nerve stimulation promotes right-to-left (R-L) shunting in the alligator. Flow patterns were investigated before and during stimulation of the intact left vagus nerve using three methods. 1) Atrial and aortic PO2 were measured simultaneously and continuously by gas probes. 2) Atrial outflows were tracked with a blood tracer (helium). 3) Flows were assessed with echocardiography. Four different flow patterns were observed before vagal stimulation: left ventricular (LV) blood flowed into both the right (RAo) and left (LAo) aortas, whereas right ventricular (RV) blood flowed only into the LAo; both aortas received a mixture of LV and RV blood; only LV blood perfused both aortas; and RV blood flowed into both aortas, but LV blood flowed only into the RAo. During vagal stimulation, both aortas received a mixture of LV and RV blood in half of the animals, and in the other half, both aortas received RV blood, but LV blood flowed only into the RAo. Doppler and contrast echocardiography demonstrated swirling flow in the foramen of Panizza and the base of the LAo during systole. These data indicate that vagal stimulation either maintains or produces R-L shunting, flow patterns are variable, and blood can swirl in the foramen of Panizza and LAo base.

Alligators and Crocodiles↗
PubMed1994

Hemodynamic comparison of microsurgical repairs for large arterial defects.

Twenty-eight femoral arteries in 14 rats were used to compare transverse closures and end-to-end anastomoses in blood vessels approximately 1 mm in diameter. The transverse closures were applied to arteriectomies created by excising one-half the circumference of the vessel over a length of 1 mm. The end-to-end anastomoses were performed after resecting a 1-mm segment. Recordings were made of pre- and postrepair flow velocity and three-point diameter measurements every 5 minutes using a 20-MHz pulsed Doppler velocimeter and digimatic caliper. Maximum reductions in flow velocity were 18% and 31% for the transverse repair and end-to-end anastomosis, respectively. Otherwise, intergroup comparisons of the postrepair normalization of both flow velocity and vessel diameter showed few significant differences (P < 0.05). We conclude that arterial defects involving no more than half the diameter of the vessel can be effectively repaired in significantly less time using the transverse closure.

Anastomosis, Surgical↗
PubMed1994

Hemodynamic effects of nasal and face mask continuous positive airway pressure.

Studies of the hemodynamic effects of nasal continuous positive airway pressure (n-CPAP) in normal subjects have had conflicting results. The largest study (n = 19) found no effect of up to 15 cm H2O on heart rate (HR), cardiac stroke volume (SV), or cardiac index. We hypothesized that n-CPAP, by increasing intrathoracic pressure, should decrease SV and cardiac output (CO) in a dose-dependent fashion in normal subjects. We also hypothesized that mouth position, i.e., open or closed, could affect intrathoracic pressure and thus SV and CO. Six normal subjects were tested with four levels of CPAP (5, 10, 15, and 20 cm H2O) under three mask conditions-face mask and nasal mask with the mouth open (mo) or with the mouth closed (mc). Noninvasive pulsed Doppler measurements of SV and HR were made under each condition. N-CPAP (mc) and face mask CPAP (f-CPAP) resulted in significant dose-dependent decreases of SV-24 +/- 5 ml (21%) and 33 +/- 5 ml (28%), respectively--from baseline to 20 cm H2O (p < 0.05). HR were unchanged and CO significantly decreased with n-CPAP(mc) and with f-CPAP, 1.6 +/- 0.38 L/min (23%) and 2.29 +/- 0.54 L/min (31%), respectively, from baseline to 20 cm H2O (p < 0.05). Esophageal pressure measurements verified increasing intrathoracic pressure with increasing levels of f-CPAP and n-CPAP (mc) but not with n-CPAP (mo). In conclusion, n-CPAP (mc) and f-CPAP resulted in significant and similar dose-dependent decreases in SV and CO.

Adult↗
PubMed1993

Hemodynamic comparison of microsurgical closures for longitudinal arteriotomies.

Twenty-four femoral arteries in 12 rats were used to compare longitudinal and transverse closures in blood vessels approximately 1 mm in diameter. The closure techniques were applied to a simple longitudinal slit, 1 mm long, and to a longitudinal defect, 0.5 mm wide and 1 mm long. Comparisons were made of the change in pre- and postrepair flow velocities, recorded every 5 min using a 20-MHz pulsed Doppler velocimeter. Maximum reductions in flow velocity (linearly related to volume flow) were 10% and 29% for the longitudinal and transverse repairs, respectively, when applied to the longitudinal slit, and 65% and 19%, respectively, when applied to the larger arteriotomy. An analysis of variance indicates that the differences in the normalization of flow velocities during the immediate postrepair period are significant (P < 0.05). We conclude that optimal flow normalization is achieved by applying the longitudinal repair to the simple slit and the transverse repair to the larger arteriotomy.

Animals↗
PubMed1993

Effects of prolonged head-down bed rest on physiological responses to moderate hypoxia.

To determine the effects of hypoxia on physiological responses to simulated zero-gravity, cardiopulmonary and fluid balance measurements were made in 6 subjects (acclimatized to 5,400 ft) before and during 5 degrees head-down bed rest (HDBR) over 8 d at 10,678 ft and a second time at this altitude as controls (CON). The VO2max increased by 9% after CON, but fell 3% after HDBR (p < 0.05). This reduction in work capacity during HDBR could be accounted for by inactivity. The heart rate response to a head-up tilt was greatly enhanced following HDBR, while mean blood pressure was lower. No significant negative impact of HDBR was noted on the ability to acclimatize to hypoxia in terms of pulmonary mechanics, gas exchange, circulatory or mental function measurements. No evidence of pulmonary interstitial edema or congestion was noted during HDBR at the lower PIO2 and blood rheology properties were not negatively altered. Symptoms of altitude illness were more prevalent, but not marked, during HDBR and arterial blood gases and oxygenation were not seriously effected by simulated microgravity. Declines in base excess with altitude were similar in both conditions. The study demonstrated a minimal effect of HDBR on the ability to adjust to this level of hypoxia.

Acclimatization↗
PubMed1992

The effect of vasodilators on pulmonary hemodynamics in high altitude pulmonary edema: a comparison.

High altitude pulmonary edema is characterized hemodynamically by a markedly restricted pulmonary vascular bed. Pulmonary vascular resistance is six to eight times higher than control values at altitude, and mean pulmonary pressure is generally elevated two to four-fold over control values. We wished to compare the effect of various vasodilators on the hemodynamics of HAPE, both to gauge their potential effectiveness in treatment of HAPE, and also to gain clues as to the mechanism of the altered pulmonary circulation. In a series of field experiments using a total of 16 subjects with HAPE and 10 well controls, we measured pulmonary hemodynamics by non-invasive Doppler echocardiography. The per cent reduction in pulmonary vascular resistance and mean pulmonary artery pressure, respectively, were 46 and 33 for oxygen, 30 and 29 for nifedipine, 29 and 25 with hydralazine, 57 and 42 with phentolamine, and 72 and 52 when oxygen and phentolamine were combined. All the vasodilators improved gas exchange, suggesting a link between edema formation and pulmonary vasoconstriction. A number of vasodilators may be useful in the treatment of HAPE; the superiority of an alpha adrenergic blocker may implicate the sympathetic nervous system in the pathophysiology of high altitude pulmonary edema.

Altitude Sickness↗
PubMed1991

Internal carotid flow velocity with exercise before and after acclimatization to 4,300 m.

Cerebral blood flow and O2 delivery during exercise are important for well-being at altitude but have not been studied. We expected flow to increase on arrival at altitude and then to fall as O2 saturation and hemoglobin increased, thereby maintaining cerebral O2 delivery. We used Doppler ultrasound to measure internal carotid artery flow velocity at sea level and on Pikes Peak, CO (4,300 m). In an initial study (1987, n = 7 men) done to determine the effect of brief (5-min) exercises of increasing intensity, we found at sea level that velocity [24.8 +/- 1.4 (SE) cm/s rest] increased by 15 +/- 7, 30 +/- 6, and 22 +/- 8% for cycle exercises at 33, 71, and 96% of maximal O2 uptake, respectively. During acute hypobaric hypoxia in a decompression chamber (inspired PO2 = 83 Torr), velocity (23.2 +/- 1.4 cm/s rest) increased by 33 +/- 6, 20 +/- 5, and 17 +/- 9% for exercises at 45, 72, and 98% of maximal O2 uptake, respectively. After 18 days on Pikes Peak (inspired PO2 = 87 Torr), velocity (26.6 +/- 1.5 cm/s rest) did not increase with exercise. A subsequent study (1988, n = 7 men) of the effect of prolonged exercise (45 min at approximately 100 W) found at sea level that velocity (24.8 +/- 1.7 cm/s rest) increased by 22 +/- 6, 13 +/- 5, 17 +/- 4, and 12 +/- 3% at 5, 15, 30, and 45 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1990

Left ventricular hemodynamics during exercise recovery.

The directional response of human left ventricular stroke volume during exercise recovery is unclear. Stroke volume has been reported to increase and decrease over exercise values during early recovery. The confounding variable may be posture. With the use of pulsed Doppler ultrasound, we tested the hypothesis that there is a significant difference between seated and supine stroke index (SI) during passive recovery from seated ergometer exercise. Thirteen subjects aged 26 +/- 2 yr performed two seated cycle ergometer exercise tests to 70% of predicted maximum heart rate (HR). Recovery was supine on one test and seated on the other. Cardiac index (CI), HR, and SI were calculated during rest, exercise, and 10 min of recovery. At rest, SI and CI were significantly (P less than 0.01) less and HR significantly (P less than 0.01) greater when the subjects were seated than when they were supine. At the last exercise work load, no significant differences were found in any measured variable between tests. During recovery, supine SI was maximal 180 s postexercise (99 +/- 14 ml/m2) and exceeded (P less than 0.01) resting supine (81 +/- 14 ml/m2) and peak exercise (77 +/- 14 ml/m2) SI by 22 and 29%, respectively. Seated SI was constant at peak exercise levels for 2 min. Seated and supine recovery CI never exceeded exercise values. Systolic and diastolic blood pressure recovery curves were similar in the two postures. We conclude that posture significantly affects SI during recovery from submaximal seated exercise. These results have implications for choice of recovery posture after stress testing in cardiac patients where it is desirable to minimize ventricular loading.

Adult↗
PubMed1989

Effects of exercise training on common femoral artery blood flow in patients with intermittent claudication.

Exercise training is a commonly used rehabilitative therapy for patients with intermittent claudication (IC). However, it is not known whether blood flow through the major conduit vessel of the leg, the common femoral artery (CFA), increases with exercise training. We tested the hypothesis that peak CFA blood flow will increase with a supervised, lengthy, and individualized exercise training program. Subjects were 10 IC patients (eight men, two women) with a mean age of 61 +/- 7 (mean +/- SD) years who had either aortoiliac (n = 7) or femoropopliteal (n = 3) stenosis. Using noninvasive Doppler flowmetry, we measured CFA blood flow and ankle pressure at rest and after a maximum symptom-limited graded treadmill test before (T1) and after 3 (T2) and 5 (T3) months of exercise training. Variables were measured in the supine and upright postures at rest and during recovery. Total walking distance and claudication distance on the treadmill were determined for T1, T2, and T3. After training, CFA blood flow and ankle pressure were not significantly higher at rest or at 1 minute after exercise compared with pretraining despite significant increases in claudication and total walking distances. The rate of CFA blood flow recovery was slower at T3, suggesting the accrual of a larger metabolic debt during exercise due to more work performed. We conclude that changes in CFA blood flow are not responsible for measured changes in performance with exercise training in IC patients.

Blood Flow Velocity↗
PubMed1989

Effect of a high-protein meal on blood flow to transplanted human kidneys.

Renal blood flow in normal adults increases after protein ingestion. The mechanisms that create this hyperperfusion are unclear. A neurogenic factor in humans has not been definitively ruled out. Accordingly, we tested the hypothesis that a high-protein meal significantly increases renal blood flow to the denervated human kidney. We studied 11 transplant recipients (TR) with denervated kidneys and 4 kidney donors (KD) with a single innervated kidney. All subjects had normal urinalysis. Using noninvasive Doppler flowmetry that was previously validated, we determined renal blood flow (RQ, ml/min) after a 12-hr fast (F) and 1, 2, and 3 hr after a high-protein meal (500 ml) of 150 g protein, 30 g fat, and 30 g carbohydrate. The RQ (mean +/- SD, ml/min) at fasting and at 1, 2, and 3 hr postprandially was 409 +/- 100, 446 +/- 100, 493 +/- 122 (P less than 0.05 vs. F), and 500 +/- 123 (P less than 0.05 vs. F), respectively, for the TR, and was 654 +/- 60 (P less than 0.05 vs. TR), 667 +/- 86 (P less than 0.05 vs. TR), 776 +/- 80 (P less than 0.05 vs. F and TR), and 809 +/- 81 (P less than 0.05 vs. F and TR) for KD. We conclude that RQ in TR increases significantly after protein ingestion. Thus, in the noninstrumented, unanesthetized human with a transplanted kidney, neural control is not a factor in the increase in renal blood flow after a high protein meal.

Cyclosporins↗
PubMed1988

Pulsed ultrasound Doppler velocimetry in the assessment of microvascular hemodynamics.

Pulsed ultrasonic Doppler velocimetry (20 MHz) (PUDVM) has evolved considerably in the last 10 years. Engineering development has resulted in a computer-controlled vessel-scanning instrument whose backscattered frequency shift spectra are analyzed using fast Fourier transforms (FFT). Benchtop and theoretic studies indicate accurate (error less than 5%) velocity and volumetric flow rate measurements in vessels with a lumen diameter as small as 1.2 mm. Clinical application of the PUDVM has provided transcutaneous measurements of blood flow variables in normal human digital arteries. Experimental application to arteries 1.0-1.5 mm has provided information on the hemodynamic effects of topical vasodilators, standard microarteriorrhaphy, variations in microvascular technique, interpositional grafts, and early wound repair. With improving computer capabilities and technical modifications, the PUDVM will be an increasingly important tool in clinical and experimental microsurgery.

Blood Flow Velocity↗
PubMed1988

Clinical evaluation versus Doppler echocardiography in the quantitative assessment of valvular heart disease.

We tested the hypotheses that Doppler echocardiography has a higher accuracy than clinical evaluation in the detection of significant aortic and mitral valvular heart disease and that Doppler echocardiography is highly accurate as compared with cardiac catheterization for the assessment of valvular disease severity. Thus, cardiac catheterization for the assessment of valve lesion severity may be unnecessary in selected patients. We prospectively evaluated 75 consecutive patients, ages 20-74 years (mean, 52 years), with clinically suspected valvular heart disease. Specific clinical and Doppler echocardiographic criteria were used to categorize each valve lesion as absent, insignificant, or significant. Criteria for a significant lesion at cardiac catheterization was an aortic or mitral valve area less than 1.1 or 1.5 cm2, respectively, or equal to or greater than 3+ cm2 aortic or mitral regurgitation at angiography. In all valve lesions, Doppler echocardiography had a higher overall accuracy than clinical evaluation. Increases in accuracies of 28%, 19%, 15%, and 7% occurred for mitral stenosis, aortic stenosis, aortic regurgitation, and mitral regurgitation, respectively, resulting in overall accuracies of 97%, 100%, 95%, and 96%. Clinical evaluation alone made 28 errors (37% of patients and 19% of valve lesions assessed), and 17 of these errors (23% of patients and 12% of valve lesions) would have resulted in inappropriate management. In only four (24%) of these 17 patients, the attending cardiologist would not have proceeded to assess the valve at cardiac catheterization.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Human left main coronary artery blood flow: noninvasive Doppler echocardiography with sample volume tracking.

We developed sample volume tracking units that controlled the pulsed ultrasonic Doppler sample volume location in relation with the anterior-posterior movement of the human left main coronary artery (LMCA). Combined with noninvasive Doppler echocardiographic mechanical sector scanners (DS), the trackers controlled the axial location of the sample volume by range gate control. The Doppler angle was minimized with the long axis of the imaged LMCA. Both stored waveform, memory-driven (MD) and real-time (RT) trackers were developed. These devices were used to measure blood velocity spectral waveforms and lumen diameters, which were used to calculate flow. Using the RT tracker, we compared DS measurements with known flows (0-1000 ml/min) in a moving 4 mm tygon tubing phantom (r = 0.92, SEE = 32 ml/min). Using the MD tracker, we compared the DS with simultaneous invasive flow measurements in 11 patients with angiographically normal coronaries and ventricular function during cardiac catheterization. Using the RT tracker, we compared the DS measurements with subsequent nonsimultaneous, invasive flow data in 8 similar patients. Invasively determined flows were calculated from angiographic diameters and blood velocities which were obtained with a Doppler velocimeter catheter. Regression coefficients (r) were: (Table: see text). V = maximum velocity, D = diameter, Q = mean flow, *p less than .05 Interoperator and intraoperator variabilities in vivo of DS measurements with RT tracking were 21% and 15%, respectively. We conclude that Doppler echocardiography with either MD or RT sample volume tracking may be of limited clinical usefulness in the noninvasive measurement of phasic left main coronary artery blood flow in unselected patients.

Angiocardiography↗
PubMed1987

Doppler predictions of pulmonary artery pressure, flow, and resistance in adults.

We examined the accuracy of noninvasive predictions of pulmonary artery pressure (P), flow (Q), and resistance (R) by means of main pulmonary artery blood velocities and diameters measured with Doppler echocardiography (DE). The ratio of noninvasive acceleration time to ejection time (An) was correlated to invasively determined mean pulmonary artery pressure (Pl) and resistance (Rl). Noninvasive flows were correlated to thermodilution flows (Ql). Simultaneous invasive and noninvasive measurements were made in nine adult patients (ages = 22 to 73 years). The results were: Pl = 87 - 152An, r = 0.90, SEE = 7 mm Hg, p less than 0.05; Rl = 899 - 1722An, r = 0.79, SEE = 121 dynes X sec X cm-5, p less than 0.05; and Ql = -0.3 + 1.21Qn, r = 0.95, SEE = 0.81 L X min-1, p less than 0.05. We then used these equations prospectively to predict Pl, Rl, and Ql in 21 of 25 (83% technically adequate) consecutive patients. Pl, Rl, and Ql ranged from 10 to 35 mm Hg, 39 to 456 dynes X sec X cm-5, and 3.51 to 8.39 L X min-1, respectively. Results were: Pl = 0.80P + 3, r = 0.72, SEE = 6 mm Hg, p less than 0.05; Rl = 0.75R - 12, r = 0.64, SEE = 77 dynes X sec X cm-5, p less than 0.005; and Ql = 0.87Q + 0.38, r = 0.83, SEE = 0.86 L X min-1, p less than 0.05. These results suggest that DE predictions of pulmonary artery pressure, flow, and resistance correlate significantly with values subsequently obtained at catheterization.

Adult↗
PubMed1987

Noninvasive Doppler assessment of human postprandial renal blood flow and cardiac output.

We compared the effects of protein, carbohydrate, or water ingestion on human renal blood flow (RBF) and cardiac output (CO). We validated and applied a noninvasive ultrasonic Doppler method to measure blood velocities and lumen diameters in the right renal artery and the ascending aorta of five healthy adults. From these measurements, we calculated the average RBF and CO over five cardiac cycles. Normalizing to body surface area, renal blood flow index to one kidney (RI) and cardiac index (CI) were calculated. The percentage of the CI distributed to a single kidney was determined as %CI = RI/CI. Subjects were studied randomly on three separate days after ingestion of each of the following equivolume (500 ml) meals: 1) 150 g protein, 30 g fat, and 30 g carbohydrate (P); 2) 150 g carbohydrate, 30 g fat, and 30 g protein (C); and 3) water. Data were obtained after 12 h of fasting and at 30, 60, 90, 120, 180, and 240 min postprandially. Analysis of covariance revealed significant (P less than 0.05) increases from fasting levels in postprandial RI at 90 to 240 min after P. Postprandial RI with P was significantly higher than with C at 180 and 240 min. Postprandial %CI with P and C decreased significantly from the fasting value at 30 to 180 min. Heart rate and mean arm cuff blood pressure did not change significantly with any diet. Results suggest that the protein-rich meal evokes a more sustained increase in postprandial RI than the carbohydrate rich meal. Despite the increase in postprandial RI, the percentage of cardiac output perfusing a kidney declines similarly with both diets.

Adult↗