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Biomedical subjects

L D Montgomery

Publications and source records attributed to L D Montgomery.

At least 37 records · Page 2Linked to original sources
PubMed1984

Thermoregulatory responses of rats to varying environmental temperatures.

The peripheral (tail) circulatory responses of six male albino rats were measured at ambient temperatures between 5 and 40 degrees C, using impedance plethysmography. Each animal was anesthetized, instrumented, and placed in a thermal environmental chamber to reach equilibrium. Tail blood flow, respiration rate, heart rate, core temperature, and tail skin temperature were then monitored at each ambient temperature. The mean tail blood flow was significantly higher (p less than 0.05) at 5 degrees C than at 10 degrees C. The mean blood flow increased significantly (p less than 0.01) at each of the temperatures above 10 degrees C. Tail skin temperature and internal body (core) temperature increased significantly with increasing ambient temperature.

Animals↗
PubMed1984

Use of impedance plethysmography to continually monitor bone marrow blood flow.

Methods for measuring bone-blood flow are often time-consuming, tedious, single-point measurements which require sacrifice of the animal. An impedance plethysmographic technique is described which can be used to quantify temporal bone marrow blood flow changes. Results obtained with the impedance technique compare favorably with the data from simultaneously administered microspheres. Injection of sympathomimetic drugs produced measurable responses: isoproterenol caused a significant increase in bone marrow blood flow within 1 min and levarterenol decreased bone marrow blood flow. Data obtained with impedance plethysmography suggest that the technique is feasible for multiple measurements on the same animal and that the technique can be used to study acute or chronic changes in bone marrow blood flow following various experimental treatments.

Animals↗
PubMed1984

Cardiovascular responses during orthostasis: effect of an increase in VO2max.

Cardiovascular responses to orthostasis were assessed in eight men (18-29 years old) before and after an 8-d cycle ergometer exercise training (E) regimen for 2 h . d-1 at 65% maximal O2 uptake (VO2 max). Each subject underwent 60 degrees head-up tilt (60 min max) before (T1) and after (T2) E. Heart rate (HR), systolic (SBP), and diastolic (DBP) pressures were measured each min before, during, and after tilt; pulse pressure (PP), mean arterial pressure (MAP), and rate-pressure-product (RPP) were calculated. Changes in plasma renin activity (PRA), vasopressin (pVP), hematocrit, hemoglobin, and plasma volume (PV, T-1824) were measured from venous blood samples taken pre- and immediately post-tilt. Following E, VO2 max increased by 8.3% (p less than 0.05), resting HR decreased by 8.1% (p less than 0.05), and PV increased by 430 ml (12.2%, p less than 0.05). Mean (+/- S.E.) tilt duration went from 40.0 +/- 5.1 min during T1 to 46.7 +/- 3.4 min during T2 (NS); mean tilt HR decreased from 86 +/- 4 bpm to 77 +/- 3 bpm (p less than 0.05), RPP decreased from 10,320 +/- 390 to 9,317 +/- 310 mm Hg . bpm (p less than 0.05), while mean SBP, DBP, PP, and MAP were unchanged. Plasma volume decreased during tilt by 479 ml in T1 compared to 544 ml in T2 (p less than 0.05), while % delta PV were similar: -13.6% and -13.9%, respectively. Peak fluid-accumulation in the calf and total leg during tilt increased (p less than 0.05) following E.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

A comparison of limb plethysmograph systems proposed for use on the space shuttle.

Comparisons of a Whitney mercury-filled double-stranded strain gauge with two plethysmographs proposed for Shuttle use--an ultrasound and an impedance plethysmograph--were performed on 20 subjects. An occlusive thigh pressure cuff, inflated to 50 mm Hg, caused partial venous occlusion and subsequent blood pooling distal to the cuff. The average maximum volume changes observed in the Whitney/ultrasound test were 2.07% and 3.35%, respectively, and 2.12% and 2.53% for the Whitney/impedance comparison. Applying the ratio of the maximum volume changes to the gain of each test system caused the impedance and ultrasound volume change determinations to be essentially identical to the Whitney gauge. The three different limb parameters measured result in significant magnitude differences but the three systems track their respective changes identically.

Adolescent↗
PubMed1980

Fluid-electrolyte shifts and thermoregulation: Rest and work in heat with head cooling.

Plasma volume and thermoregulatory responses were measured, during head and neck cooling with a liquid-cooled neoprene headgear, in four men (21-43 years old) during 60 min of rest, 60 min of ergometer exercise (45% VO2 max), and 30 min of recovery in the supine position at 40.1 degrees C DBT and 40% rh. Compared with control (noncooling) responses, cooling decreased thigh sweating and increased mean skin temperature (Tsk) at rest, and attenuated the increases in thigh sweating by 0.26 mg/min x cm2 (-22.4%, p < 0.05), heart rate by 10 b/min (-8.5%, N.S.), rectal temperature (Tre) by 0.3 degrees C (N.S.), and ventilation by 12.5% (N.S.) during exercise. In recovery, cooling facilitated the decreases in thigh sweat rate, heart rate, Tre, and forearm blood flow, and enhanced the increase in Tsk toward control levels. Cooling had no effect upon plasma protein, osmotic, or electrolyte shifts during rest, exercise, or recovery. Plasma volume (PV) loss during exercise was 11.2% without cooling and 10.9% with cooling. Cooling increased PV by 3% (p < 0.05) during rest, and this differential was maintained throughout the exercise and recovery periods.

Adult↗
PubMed1977

Variation of forearm, hand, and finger blood flow indices with ambient temperature.

Impedance plethysmography was used to measure bilateral blood flow in the forearms, hands, and digits of seven healthy male subjects. The objectives were to determine the degree of symmetry between right and left body segments and to quantify the extent of vasomotor change at ambient temperatures ranging from 10 degrees to 46 degrees C. The mean forearm blood flow index ranged from 3.9 ml/(100 ml . min) at 10 degrees C to 7.5 ml/(100 ml . min) at 46 degrees C. Mean hand blood flow indices increased from 1.6 ml/(100 ml . min) at 10 degrees C to 10.7 ml (100 ml . min) at 46 degrees C. Finger blood flow indices in the proximal and medial phalanges of the five digits ranged from less than 1.0 ml/(100 ml . min) at 10 degrees C to over 27.0 ml/(100 ml . min) at 46 degrees C. Although each subject demonstrated variations in right and left side blood flow during any selected experiment the grouped mean flow indices exhibited no statistically significant side dominance. These experiments quantify the vasomotor alterations in the upper extremities and indicate that the more distal body segments exhibit relatively larger vasomotor responses to changes in ambient temperature than do the more proximal body segments.

Blood Flow Velocity↗
PubMed1977

Cardiovascular responses of men and women to lower body negative pressure.

Changes in blood flow and blood redistribution were measured by impedance plethysmography in the pelvic and leg regions of six male and four female subjects during three 5-min exposures to -20, -40, and -60 mm Hg lower body negative pressure (LBNP). Female subjects demonstrated significantly higher mean heart rate and lower leg blood flow indices than the male subjects during the recumbent control periods. Men had slightly higher mean resting systolic and diastolic blood pressures and higher mean control pelvic blood flow indices. Women demonstrated significantly less blood pooling in the legs and slightly less in the pelvic region than the men. All of the 18 tests with male subjects at -60 mm Hg were completed without initial signs of syncope, while only two of the tests with women were completed successfully without the subject exhibiting presyncopal conditions. The results of this study indicate that impedance plethysmography can be used to measure segmental cardiovascular responses during LBNP and that females may be less tolerant to -60 mm Hg LBNP than males.

Atmospheric Pressure↗
PubMed1976

Comparison of an impedance device to a displacement plethysmograph for study of finger blood flow.

Empirical values of finger blood flow, determined with a commercial electrical impedance device, were compared with blood flow measurements made with a pulsatile air displacement plethysmograph. The measurements were made on the medial phalanges of the first, second, and third fingers of the left and right hands. Blood flow indices were calculated from extrapolated slopes of the recorded impedance and mechanical changes occurring during systole. Two series of observations were made on seven healthy male subjects. The first series consisted of 33 simultaneous measurements with the impedance rheograph and the air displacement plethysmograph on the same finger segment. In the second series of experiments, 16 measurements were made on comparable segments with the rheograph on one side of the body and the air displacement plethysmograph on the other side. The positions of the mechanical and electrical transducers were then exchanged and the procedure repeated. The right and left results were then averaged for each of the two flow measurement systems. Blood flow indices, determined with the impedance rheograph, were consistently 30% lower than those obtained with the air displacement system. The overall mean (+/- S.E.) for the impedance to air displacement blood flow ratio for the first series of measurements was 0.69 +/- 0.03 (range = 0.46 to 1.02). The mean (+/- S.E.) impedance to air displacement ratio for the second series of experiments was 0.68 +/- 0.06 (range = 0.30 to 1.14).

Adult↗
PubMed1975

Biothermal simulation of scuba divers.

A biothermal model of the immersed man is presented and validated. Comparisons are made between analytic and experimental values of temperature-vs-time profiles for neck-immersed seminude and wet-suited subjects. An engineering example is presented to demonstrate how the model may be used to evaluate proposed life-support system designs.

Body Temperature Regulation↗
PubMedDate not supplied

Body volume changes during simulated microgravity: auditory changes, segmental fluid redistribution, and regional hemodynamics.

Space adaptation syndrome (SAS), manifested by cephalad fluid shifts, spacial disorientation, nausea, and vomiting, is of varied expression and uncertain etiology. One theory is that fluid shift to the upper body alters the function of the vestibular apparatus to create an entity similar to Meniere's disease. Since clinical vestibular dysfunction syndromes are mirrored by altered cochlear function, this experiment was undertaken to study the relation between fluid redistribution and the auditory effects of initial antiorthostatic bed rest. Manual and bone audiometry, impedance tympanometry, and brain-stem evoked potentials were used to monitor auditory changes prior to, during, and following short term exposure to -6 degrees head down tilt. Impedance plethysmography was performed to assess the segmental and intracranial fluid redistribution and hemodynamic changes during short-term head down tilt simulated microgravity. Even though significant cephalad fluid shift produced marked intracranial congestion and the subjects exhibited SAS symptoms, no clinically significant changes in the auditory system could be detected.

Acoustic Impedance Tests↗
PubMedDate not supplied

Hemodynamic and thermal responses to head and neck cooling in men and women.

Personal cooling systems are used to alleviate symptoms of multiple sclerosis and to prevent increased core temperature during daily activities. The objective of this study was to determine the operating characteristics and the physiologic changes produced by short term use of one commercially available thermal control system. A Life Support Systems, Inc. Mark VII portable cooling system and a liquid cooling helmet were used to cool the head and neck regions of 12 female and 12 male subjects (25-55 yr) in this study. The healthy subjects, seated in an upright position at normal room temperature (approximately 21 degrees C), were tested for 30 min with the liquid cooling garment operated at its maximum cooling capacity. Electrocardiograms and scalp and intracranial blood flows were recorded periodically during each test sequence. Scalp, right and left ear, and oral temperatures and cooling system parameters were logged every 5 min. Scalp, right and left ear canal, and oral temperatures were all significantly (P <0.05) reduced by 30 min of head and neck cooling. Oral temperatures decreased approximately 0.2-0.6 degrees C after 30 min and continued to decrease further (approximately 0.1-0.2 degrees C) for a period of approximately 10 min after removal of the cooling helmet. Intracranial blood flow decreased significantly (P < 0.05) during the first 10 min of the cooling period. Both right and left ear temperatures in the women were significantly lower than those of the men during the cooling period. These data indicate that head and neck cooling may be used to reduce core temperature to that needed for symptomatic relief of both male and female multiple sclerosis patients. This study quantifies the operating characteristics of one liquid cooling garment as an example of the information needed to compare the efficiency of other garments operated under different test conditions.

Adult↗
PubMedDate not supplied

Physiologic and thermal responses of male and female patients with multiple sclerosis to head and neck cooling.

Personal cooling systems are used to alleviate symptoms of multiple sclerosis and to prevent increased core temperature during daily activities. The objective of this study was to determine the thermal and physiologic responses of patients with multiple sclerosis to short-term maximal head and neck cooling. A Life Support Systems, Inc. Mark VII portable cooling system and a liquid cooling helmet were used to cool the head and neck regions of 24 female and 26 male patients with multiple sclerosis in this study. The subjects, seated in an upright position at normal room temperature (approximately 22 degrees C), were cooled for 30 min by the liquid cooling garment, which was operated at its maximum cooling capacity. Oral, right, and left ear temperatures and cooling system parameters were logged manually every 5 min. Forearm, calf, chest, and rectal temperatures, heart rate, and respiration rate were recorded continuously on a U.F.I., Inc. Biolog ambulatory monitor. This protocol was performed during the winter and summer to investigate the seasonal differences in the way patients with multiple sclerosis respond to head and neck cooling. No significant differences were found between the male and female subject group's mean rectal or oral temperature responses during any phase of the experiment. The mean oral temperature decreased significantly (P < 0.05) for both groups approximately 0.3 degrees C after 30 min of cooling and continued to decrease further (approximately 0.1-0.2 degrees C) for a period of approximately 15 min after removal of the cooling helmet. The mean rectal temperatures decreased significantly (P < 0.05) in both male and female subjects in the winter studies (approximately 0.2-0.3 degrees C) and for the male subjects during the summer test (approximately 0.2 degrees C). However, the rectal temperature of the female subjects did not change significantly during any phase of the summer test. These data indicate that head and neck cooling may, in general, be used to reduce the oral and body temperatures of both male and female patients with multiple sclerosis by the approximate amount needed for symptomatic relief as shown by other researchers. However, thermal response of patients with multiple sclerosis may be affected by gender and seasonal factors, which should be considered in the use of liquid cooling therapy.

Activities of Daily Living↗
PubMedDate not supplied

Physiologic and functional responses of MS patients to body cooling.

OBJECTIVE: The objective of this study was to compare the responses of multiple sclerosis (MS) patients to short-term cooling therapy using three different vest configurations. DESIGN: Each garment was used to cool 13 male and 13 female MS subjects (31-67 yr). Oral and right and left ear temperatures were logged manually every 5 min. Arm, leg, chest, and rectal temperatures, heart rate, and respiration were recorded continuously on a Biolog ambulatory monitor. Each subject was given a series of subjective and objective evaluation tests before and after cooling. RESULTS: The Life Enhancement Technologies and Steele vests test groups had similar, significant (P < 0.01) cooling effects on oral and ear canal temperatures, which decreased approximately 0.4 degrees C and 0.3 degrees C, respectively. The Life Enhancement Technologies active liquid cooling vest produced the coldest (P < 0.01) skin temperature and provided the most improvement on subjective and objective performance measures. CONCLUSIONS: These results show that the various garment configurations tested do not produce similar thermal responses in all MS patients. The circulating liquid cooling vest was found to be more effective than either of the two passive cooling garments tested.

Activities of Daily Living↗