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H S Ho

Publications and source records attributed to H S Ho.

At least 55 records · Page 3Linked to original sources
PubMed1993

The effects of CO2 pneumoperitoneum on hemodynamics in hemorrhaged animals.

BACKGROUND: Carbon dioxide (CO2), the primary gas currently used for pneumoperitoneum, has been known to cause systemic effects on acid-base balance and hemodynamic stability. We studied the hemodynamic effects of CO2 pneumoperitoneum in a hemorrhagic shock model to assess the safety of laparoscopic procedures in acute trauma patients. METHODS: After 1 hour of baseline, 32 anesthetized adult pigs were randomized into four groups. Group 1 animals had no hemorrhage, serving as a control group. Group 2 animals had a mild hemorrhage of 10 ml/kg/hr. Group 3 animals had a moderate hemorrhage of 20 ml/kg/hr. Group 4 animals had a moderate hemorrhage but were resuscitated with 40 ml/kg of lactated Ringer's solution. All animals were then insufflated to an intraabdominal pressure of 15 mm Hg with CO2 gas for 1 hour. The abdomen was then decompressed, and the animals were observed for another hour. All animals survived hemorrhage. One death each occurred in moderate hemorrhage groups, both near the end of CO2 pneumoperitoneum. These animals were not included in statistical analysis. RESULTS: In euvolemic animals, CO2 pneumoperitoneum induced hypercapnia (from 34 +/- 1 mm Hg to 48 +/- 1 mm Hg), acidemia (from 7.45 +/- 0.02 to 7.36 +/- 0.02), and a 20% reduction in stroke volume. Mild hemorrhage and CO2 insufflation resulted in a similar degree of acidemia (7.35 +/- 0.01), but moderate hemorrhage and CO2 insufflation led to more severe acidemia (7.26 +/- 0.02). Fluid resuscitation failed to prevent this severe fall in pH (7.30 +/- 0.03) for group 4. PaCO2 was not affected by hemorrhage, but CO2 pneumoperitoneum induced significant hypercapnia in all groups, ranging from 48 +/- 1 mm Hg for euvolemic animals to 52 +/- 1 mm Hg for moderate hemorrhage animals. Stroke volume declined as a function of blood loss, and it was further depressed by CO2 insufflation, to as low as 75% of baseline in mild hemorrhage and 55% of baseline in moderate hemorrhage. Both stroke volume and cardiac index initially responded to large-volume fluid replacement after moderate hemorrhage but quickly decreased to levels comparable to those of unresuscitated animals when CO2 pneumoperitoneum was created. CONCLUSIONS: Intraperitoneal insufflation with CO2 for diagnostic laparoscopy may be hazardous in acute hypovolemic trauma patients.

Animals↗
PubMed1992

Intraperitoneal carbon dioxide insufflation and cardiopulmonary functions. Laparoscopic cholecystectomy in pigs.

We studied the effects of laparoscopic cholecystectomy on respiratory and hemodynamic function in eight adult pigs. Minute ventilation was adjusted to normalize baseline arterial blood gases, then fixed throughout carbon dioxide insufflation. A metabolic measurement cart recorded total CO2 excretion, oxygen consumption, and minute ventilation. Carbon dioxide pneumoperitoneum was maintained at a constant pressure of 15 mm Hg as cholecystectomy was performed. After 1 hour of insufflation, CO2 excretion increased from 115 +/- 10 mL/min to 149 +/- 9 mL/min but O2 consumption remained unchanged. The PaCO2 increased from 35 +/- 2 mm Hg to 49 +/- 3 mm Hg and arterial pH fell from 7.47 +/- 0.02 to 7.35 +/- 0.03. Systemic and pulmonary hypertension occurred and stroke volume dropped from 35.5 +/- 3.5 mL to 28.6 +/- 2.2 mL with compensatory tachycardia. Right atrial pressure remained unchanged as inferior vena cava pressure increased to reflect the intraperitoneal pressure. We conclude that CO2 pneumoperitoneum resulted in significant transperitoneal CO2 absorption, with secondary hypercapnia and acidemia. The accumulation of CO2 was also associated with an increase in systemic and pulmonary arterial pressure. Heart rate increased to compensate for the decreased stroke volume to maintain cardiac output.

Acid-Base Equilibrium↗
PubMed1988

Comparative study of shortwave heating patterns in phantoms with polyethylene and silk partitions.

Specific absorption rate (SAR) and effective depths of heating patterns induced by a shortwave, pancake diathermy applicator in fat-muscle phantom are measured. Midplane partitions of polyethylene and silk screen with and without contact chemicals are used. Thermographically obtained SAR data show nearly the same value for silk-screen partitions with and without contact chemicals and slightly lower values with polyethylene partitions, provided that the partition midplanes are tightly pressed against each other. Thermometry data indicate that for low-power exposures the major error in thermographic measurements obtained after termination of heating is due to thermal diffusion and not evaporative cooling in the opened midplane of the phantom.

Diathermy↗
PubMed1986

Small-volume resuscitation with hypertonic saline dextran solution.

Small-volume hypertonic resuscitation has been proposed as an effective means for restoration of cardiovascular function after hemorrhage at the scene of an accident. We evaluated the cardiovascular, metabolic, and neurohumoral response of resuscitation after hemorrhage using 200 ml of 2400 mosm sodium chloride, 6% dextran 70. Unanesthetized adult sheep were bled to maintain mean arterial pressure at 50 mm Hg for 3 hours, shed blood volume = 42 +/- 7 ml/kg. The sheep were then treated with a single bolus infusion of hypertonic saline dextran (n = 7) or normal saline solution (control group, n = 7) and then observed for a 30-minute period of simulated patient transport during which no additional fluid was given. Hypertonic saline dextran caused rapid restoration of blood pressure and cardiac output within 2 minutes of infusion. Cardiac output remained at or above baseline level, while both O2 consumption and urine output increased to above baseline level during the 30 minutes of simulated patient transport. By comparison 200 ml of normal saline solution caused only a small increase in blood pressure and no improvement in cardiac output or oxygen consumption. After this 30-minute period, both groups were given lactated Ringer's solution as needed to return and maintain cardiac output at its baseline value. The volume of lactated Ringer's solution required to maintain cardiac output was less in the hypertonic group, 371 +/- 168 ml, only one sixth that of the control group, 2200 +/- 814 ml. In summary after 3 hours of hypovolemia, a small volume of hypertonic saline dextran, about 4 ml/kg, fully restored cardiovascular and metabolic function for at least 30 minutes and significantly lowered the total volume requirements of resuscitation.

Animals↗
PubMed1980

Biologic effects of microwave exposure. II. Studies on the mechanisms controlling susceptibility to microwave-induced increases in complement receptor-positive spleen cells.

In attempting to evaluate the mechanisms responsible for susceptibility to the inductive increase in splenic complement receptor-positive (CR+) cells following exposure to 2450-MHz microwaves, it was found that sensitivity to microwave-induced CR+ cell increases was under genetic control. In particular, evidence was accumulated suggesting that regulation was under the control of a gene or genes closely associated with but outside of the mouse major histocompatibility complex (H-2). All responsive strains of mice tested were of the H-2k haplotype, while mice of the H-2a, H-2b, H-2d and H-1i5 haplotypes were refractory to the microwave-induced increases in CR+ cells. By utilizing certain H-2k strains of mice that were genetically unable to respond to endotoxin, we were able to show that these strains of mice responded to microwaves, but not to endotoxin, by increasing CR+ cells. Microwave-induced increases in CR+ cells were not mimicked by the intraperitoneal injection of hydrocortisone. Athymic mice responded to microwave exposure, indicating that this event was not regulated by the T-cell population. Mice less than eight weeks old were found not to be susceptible to exposure to 2450-MHz microwaves. These studies indicate that microwaves do induce changes in the population of cells with specific cell-surface receptors, that susceptibility to these changes is under genetic control, and that it is unlikely that endotoxin, corticosteroids, or regulatory T cells play a significant role in the mechanisms regulating these increases.

Aging↗
PubMed1979

The effect of environmental temperature and average dose rate of microwave radiation on the oxygen-consumption rate of mice.

The oxygen consumption rate of CF1 male mice was determined before, during, and after sham- and microwave-irradiation at environmental temperatures of 20 degrees C, 24 degrees C, 30 degrees C, and 35 degrees C, relative humidity of 55%, and air flow rate of 78 ml/min. Five forward power levels ranging from 0.09 to 3.3 W, which resulted in corresponding average dose rates ranging from 1.2 to 45.1 mW/g were used. The values of the oxygen consumption rate were converted to those of the specific metabolic rate (SMR). The result indicates that with high levels of microwave dosing (greater than 10 mW/g) the specific metabolic rate of mice decreased in some cases, in the environmental temperatures of 20 degrees C and 24 degrees C. However, the decreased SMR values were not lower than the SMR values of the sham-irradiated group in 30 degrees C. In the case of 35 degrees C, the high level dosing with microwave radiation caused increases in the SMR value over the sham value. A possible trend towards increased SMR value during and after irradiationwith low level (1.6 mW/g) microwave radiation in the environmental temperatures of 24 degrees C and 30 degrees C suggests further experiments with low level microwave radiation to determine possible effects of low level microwave radiation in stimulating increases in specific metabolic rate.

Animals↗
PubMed1977

Heat-dissipation rate of mice after microwave irradiation.

The heat dissipation rate from individual CF1 male mice was determined by a bio-calorimeter before and after exposure to microwave radiation. The animals were irradiated singly in an environmentally-controlled waveguide apparatus with 2450 MHz CW microwave radiation. The incident power levels were 0 (sham), 0.4, 0.8, 1.7 and 3.3 W, which resulted in corresponding mean average absorbed dose rates of 0 (sham), 7, 12, 27 and 39 mW/g. The environmental conditions were 24 degrees C temperature, and 50% relative humidity. The results indicate an increased heat-dissipation rate of the animals (compared to sham) for average absorbed dose rates above 12 mW/g.

Animals↗
PubMed1975

Contrast of dose distribution in phantom heads due to aperture and plane wave sources.

Current microwave biologic effects research uses both aperture and plane wave sources. In this theoretic investigation, the dose rate (time rate of energy absorption per unit mass) patterns are compared between phantom heads irradiated by both microwave sources. Two brain tissue-equivalent spheres with radii of 3.3 and 7 cm are used to simulate monkey and human heads, respectively. In addition, a five-layered tissue-equivalent sphere is employed to simulate more closely the various tissues in a monkey head. Theoretic formulations of dose rate patterns in multi-layered tissue-equivalent spheres due to separate plane wave and aperture source treatments are derived from the summation of spherical harmonics technique. Calculations are made for the dose rate patterns along two cross-sectional planes and three rectangular axes in the spheres. The results of these calculations indicate variations in dose rate patterns for different sources and phantom head sizes. For aperture irradiation, microwave energy penetration into the phantom heads appears weak compared to the "hot spots" prominent in the plane wave exposure situation. It is concluded that for different radiation sources, direct comparison of biologic results by external field measurements as the only common denominator may not be dosimetrically valid. The results also indicate that for the same measured exposure rate (power density), the microwave energy absorption pattern in a human head may vary according to the type of radiation source.

Animals↗
PubMed1975

Dose rate distribution in triple-layered dielectric cylinder with irregular cross section irradiated by plane wave sources.

Previous investigations have shown that absorptions of microwave energy in biological bodies depend, in part, on the size and shape of the biological bodies. Calculations of dose rate distributions in regularly-shaped biological tissues have been reported. In this investigation, dose distributions are calculated for a human thigh simulated by a dielectric cylinder with irregular cross section. Method of moments is used in the investigation. The results indicate possibility of using method of moments to calculate dose distribution in a two-dimensional irregularly-shaped biological body. It is concluded that additional research is needed to determine dose rate distribution in three-dimensional irregularly-shaped biological bodies.

Mathematics↗