PMC

The airflow trace (bottom trace) is uncalibrated, with inspiratory flow upwards. As in Fig. , the upper trace shows the integrated inspiratory airflow signal, with a 10 μL calibration bar shown in the inset. A, thermoneutral conditions (T _chamber = 33°C). B, T _chamber of 43°C. C, during sustained gasping. D, recovery from gasping (T _chamber = 33°C).

Changes in T _core and T _chamber in saline‐exposed (A) and DNE pups (B) under thermoneutral conditions (T _chamber = 33°C), and during moderate thermal stress (T _chamber = 37.5°C). Each animal is represented twice: once at a T _chamber of 33°C and once at 37.5°C. There are 72 pups in each treatment group, resulting in 144 observations in each group. For a detailed explanation, see text.

The airflow trace (bottom trace) is uncalibrated, with inspiratory flow upwards. The upper trace shows the integrated inspiratory airflow signal, with a 100 μL calibration bar in the inset. One apnoea is shown, which is defined as the absence of breathing for greater than or equal to two cycle periods recorded under thermoneutral conditions.

Individual values for (A), (B) and RER (C) at a T _chamber of 33 and 37.5°C in saline (filled circles) and DNE (open squares) pups. There were no significant treatment effects, although the temperature effect was significant for in control animals. *, different from 33°C within a treatment group (P < 0.05).

The weight corrected pulmonary ventilation rate under baseline (thermoneutral) conditions, plotted as a function of the litter from which animals were derived. The data represent the experiments from protocol 1 (Table ), where 13 saline‐exposed control litters and 13 DNE litters were used. The regression line (continuous line) and 95% confidence limits are included. Neither regression slope differed from zero, which is consistent with an absence of litter effects. Moreover, the variance within litters is similar to the variance between litters. For more details, see text.

Individual values for (A), V _T (B) and frequency (C), at T _chamber of 33 and 37.5°C, in saline (filled circles) and DNE (open squares) pups. did not change with temperature, although it was lower in DNE pups at each T _chamber. This was the result of a lower V_T (B) at a T _chamber of 37.5°C. There were no treatment or temperature effects on breathing frequency. ^#, DNE different from saline (P < 0.05). Horizontal lines represent the group mean value.

A, head‐out plethysmography. Temperature is servo‐controlled with a heat lamp and control unit. Flow entering and exiting the chamber with breathing passed through a pneumotachometer that was connected to a differential pressure transducer. The voltage output from the pressure transducer was sent in parallel to an A/D board and an analogue integrator that was set to record inspired flow. The output from the analogue integrator was also sent to the A/D board, and inspired breath volume was calibrated by injecting known volumes of air into the chamber. B, whole‐body plethysmography was used to record metabolic rate. An analyser pulled gas through the chamber and across Dri‐rite and the O₂ and CO₂ analysers. Chamber gas flow was monitored by a pneumotach placed in series with the analyser flow output. The pneumotachometer was calibrated with a rotameter. Voltage outputs from the pressure transducer (flow) and the O₂ and CO₂ analysers were sent to the A/D board for visualization and analysis.

Individual values showing the number of apnoeas in 10 min (A) and the duration of each apnoea (B) at a T _chamber of 33 and 39°C in saline (filled circles) and DNE (open squares) pups. Two‐way ANOVA revealed a significant temperature effect for apnoea number, although no treatment effects or temperature‐treatment interaction, indicating that both treatment groups had more apnoeas with heating (see text). There was a significant treatment effect for apnoea duration at 33°C but not at 37.5°C. ^#, DNE different from saline (P < 0.05). Horizontal lines represent the group mean value.

A–D, T _core and ventilatory response to severe thermal stress in saline‐exposed (filled circles) and DNE (open squares) pups. T _chamber was 33°C at baseline, and then increased to 43°C, and was maintained at that level until gasping ensued. Thirty seconds after gasping onset, T _chamber was adjusted back to 33°C, and recovery data were recorded for 20 min. T _core was measured after the 20 min recovery period ended. To obtain values for peak T _core at a T _chamber of 43°C, this protocol was repeated in six rats (three saline and three DNE), although the pups were removed directly after the onset of gasping so that T _core could be measured. ^#, DNE different from saline (P < 0.05); *, different from 33°C within a treatment group (P < 0.05). Horizontal lines represent the group mean value.