We present new ASCA observations covering the 0.5-10 keV X-ray range of the cooling neutron star candidates PSR 0656ϩ14 and PSR 1055Ϫ52. Previous ROSAT observations had shown that two-component models, either two blackbodies or a blackbody plus a power-law, provided the best spectral fits to their X-ray emission. The combined ASCA and ROSAT spectrum of PSR 0656ϩ14 reveals two blackbody components with T 2 8 ϫ 10 5 K and T 2 1.5 ϫ 10 6 K and shows evidence that a power-law component is needed to account for higher energy photons. This three-component fit gives a reduced 2 that is half the value of a more conventional two component fit (1.3 as compared to 2.4). The fit to the combined spectrum for PSR 1055Ϫ52 yields a two-blackbody fit with T 2 8 ϫ 10 5 K and T 2 3.7 ϫ 10 6 K. Our results favor the existence of a hot polar cap in each of these pulsars with the ratio of the polar cap area to the neutron star surface area being 7 ϫ 10 Ϫ3 and 3 ϫ 10 Ϫ5 for PSR 0656ϩ14 and PSR 1055Ϫ52, respectively. The results are compared to models that make predictions of polar cap heating processes.
This paper reports the expired minute-ventilation (VE) responses of 5 subjects to three step levels in a) work rate on a bicycle ergometer (30, 50, and 70 W), b) inhaled constant fraction (CF) of CO2 (3, 5, and 7%), and c) inhaled constant flux (CFlux) of CO2 (0.3, 0.4, and 0.5 l/min (STPD) injected in the inspired air-stream). Both exercise (isocapnic with regulated PETCO2) and CFlux provoke larger and similar steady-state responses in VE, than CF. Both the CF and CFlux responses are hypercapnic, but the CFlux responses show evidence of "hypercapnic regulation." VE and total CO2 input into the alveoli (i.e., VCO2 plus inhaled CO2) are excellently correlated in both the CF and the CFlux cases. However, the CFlux delivery provokes a far greater VE for a given total input of CO2 than CF, and the CFlux response resembles the VE/VCO2 plot of exercise. We conclude that CFlux inhalation of CO2 simulates the metabolic CO2 production rate of exercise, and thus the humoral aspects of exercise hyperpnea in the steady state.
In five persons the transient ventilatory response was measured to three step levels of exercise, inhaled constant fraction of CO2, and inhaled constant flux of CO2. With constant CO2 fraction inhalation (3, 5, and 7%), the transient response of the minute-ventilation (VE) is associated with on- and off-time delays (Td). Our Td periods include equipment delay, and our bolus inhalations by constant flux provoke on- and off-Td's of 6-8 s, which approximate to the transport delay of blood passing from the alveoli to the peripheral chemosensitive areas. With exercise (30, 50, and 70 W) we found a fast rise in VE (i.e., mainly in respiratory frequency) within the first breath, but no detectable on- and off-Td. The ventilatory responses to exercise are equal to those of constant CO2 flux inhalation. We modeled PACO2 oscillations, which occur through a respiratory cycle, and show that the oscillations provoked by constant CO2 flux have modified timing, amplitude, and slope compared with those of constant CO2 fraction. The increase in ventilation is the same when the CO2 is achieved by constant flux inhalation at rest or by exercise.
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