Estimated maximum failure rates of cycle monitors using daily conception probabilities in the menstrual cycle.

BACKGROUND: A number of menstrual cycle monitors have been developed to detect the fertile window of the menstrual cycle, mainly for contraceptive purposes. Reliable data on most of these systems are still missing but are urgently needed because many women use them and the tested systems differ enormously in price and effectiveness. We suggest a new efficacy estimating method to evaluate cycle monitors prior to full prospective clinical trials. METHODS: Sixty-two women prospectively tested seven cycle monitors and the symptothermal method (STM) of natural family planning (NFP) but not more than two different systems at the same time. The clinical fertile window was determined by detecting the day of ovulation using daily urinary LH measurements and daily ultrasonic folliculometry. This was compared to the fertile phase predicted by the systems. Maximum failure rates were estimated for each cycle monitor and the STM, using the daily conception probability rates taken from the European Fecundability Study. Intercourse was assumed to occur on each of all falsely predicted days of infertility. RESULTS: Sixty-two women with a mean age of 31 years (range: 21-42 years) contributed a total of 122 cycles to this study. Monitors based on the microscopic evaluation of saliva or mucus had many more false infertile days than the other methods based on temperature or hormonal measurements (225 versus 42 days). The maximum unintended pregnancy rates per cycle for temperature computers were estimated to be 0.0134-0.0336, for the hormonal computer 0.1155 and for mini-microscopes 0.2313-0.2369. For the STM of NFP, there were no false infertile days. CONCLUSIONS: The STM of NFP proved to be the most effective contraceptive method to detect the fertile window among all the methods tested. The estimated efficacy of the other cycle monitors range from the temperature computers (upper level) to the hormonal computer (medium level) and the mini-microscopes with very low estimated contraceptive efficacy.

The effect of graded immersion on heart volume, central venous pressure, pulmonary blood distribution, and heart rate in man.

The present experiments have been conducted to study the immediate effects of graded immersion on the central circulation. When taking heart volume as an indicator, it was found that immersion to the diaphragm of a standing subject produces the same changes as assumption of the supine posture. Heart volume increases by approximately 130 ml. When the water level is raised to the neck, an extra pressure corresponding to a water column extending from the diaphragm to the surface of the water of approximately 25 cm H2O forces blood into the thorax. The heart becomes distended by an additional 120 ml. Correspondingly the central venous pressure at the height of the right atrium increases from 2.5 to 12.8 mm HG when the water level rises from the diaphragm to the neck. The greater filling of the pulmonary circulation is accompanied by a decrease in vital capacity and visualized by scintigrams. The preferential increase in blood volume of the apical regions is striking. When raising the water level from the symphysis to the xiphoid heart rate falls by about 15%.

Time course of cardiac distension with rapid immersion in a thermo-neutral bath.

13 subjects standing in a narrow upright tank were exposed to rapid water immersion up to the neck. The tank was filled from an elevated reservoir in less than 4 s. In 8 subjects heart size was measured by Roentgen-cinematography combined with video tape recording. Planimetry of the diastolic postero-anterior area of the heart showed an average increase in heart size of 30% within 6 s. In 5 subjects central venous pressure and the height of hydrostatic pressure in the tank were recorded. The two pressures rose and fell simultaneously without delay when the hydrostatic pressure exceeded the level of the diaphragm. Rapid immersion caused a fall in heart rate of approximately 20%. The findings speak in favor of the concept that the right heart does not constitute a resistance and that the pulmonary circulation and the systemic capacitance vessels form a functional unit.

Effective compliance of the circulation in the upright sitting posture.

The effective compliance is defined as the relation of change in blood volume to change in central venous pressure. It was measured in 8 upright sitting male subjects and amounted to 3.3 ml/(mm Hg X kg BW). It is, therefore, by about 50% greater than the effective compliance in the supine subject which amounts to 2.3 ml/(mm Hg X kg BW). . This difference is probably due to the posture dependent blood volume distribution in the low pressure system whose "upper" and "lower" sections have nonlinear pressure-volume characteristics. Immersion to the neck reduces the effective complicance to about half the control value (1.9 ml/(mm Hg X kg BW) which probably constitutes the effective compliance of the intrathoracic circulatory compartment.