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The time course of $$\dot V$$ a and $$PA_{CO_2 }$$ has been observed in two healthy subjects during moderate muscular exercise, and during inhalation of CO either at constant fraction or at constant flow rate. Six experiments of each type have been done on each subject. The effects of the two methods of inhalation should be a priori different. Inhalation of CO at constant fraction induces an extra load of CO increasing with ventilation. On the contrary, inhalation of CO at constant flow rate induces constant extra load of CO independent of ventilation as does muscular exercise at constant power. Thus it can be predicted that with inhalation at constant flow rate and with muscular exercise at constant power the time course of the transients should be similar and their duration shorter than with inhalation at constant fraction. This is confirmed by the experiments. The steady state is not reached after 30 min of inhalation. The gain of the system (Δ $$\dot V$$ a/Δ $$PA_{CO_2 }$$ ) increases with time in one subject with a constant level of consciousness, it decreases with the decrease of consciousness in an other subject. [ABSTRACT FROM AUTHOR]

Continuous positive airway pressure devices are routinely used to treat sleep breathing disorders. Automated devices that adjust the therapeutic pressure have recently been proposed. The utility of such devices is still controversial, as rigorous clinical comparisons are difficult to perform as a result of patient and device differences. The current authors studied automated devices in a respiratory model that was able to mimic upper airway mechanics and to interact with pressure adjustment in a closed loop. Five auto-adjusted devices were submitted to this model, in order to determine their ability to detect respiratory events and adjust pressure accordingly. All apnoeas were suppressed, whilst the reaction to repetitive hypopnoeas was dependent on the airflow shape. In some devices, repetitive hypopnoeas were changed to flow limitation. Artificial snoring caused a pressure increase in four devices, and constant mask leak was not systematically compensated. Only one device did not raise pressure in response to central apnoeas with opened upper airways. These findings show that, in some devices, event classification failed and normal airflow was not fully restored, resulting in elevated residual event indices. In conclusion, this model is useful in order to reproducibly compare diagnostic and therapeutic capacities of commercial devices as a first step, before costly clinical studies.

In the operant conditioning experiment described by HEFFERLINE et al. (1959) a subject terminates or postpones an aversive noise stimulation by producing a particular myoelectrical activity (operant response : OR). These authors observe an increase of OR occurrence frequency in subjects ignoring the aim of the experiment (naive subjects), and they come to the conclusion that this method is efficient. Nevertheless, the validity of this conclusion is questioned by the lack of control experiments. Hence, this work has to be restudied. We have submitted 13 subjects to a control experiment. Subjects were placed under conditions similar to those used by HEFFERLINE et al., but without any contingency relating the myoelectric activity with the aversive stimulus. The results of these open-loop experiments showed that in a given subject, OR occurrence frequency may vary in large proportions as a function of time. In HEFFERLINE's naive subjects, the increase of occurrence frequency remained completely within the limits of spontaneous variations observed in our control subjects. Therefore, this increase is not significant. We have submitted 18 subjects to a conditioning experiment. 14 subjects among them produced more OR than those of the control subjects during the closed-loop experiment. We conclude that these 14 subjects have been actually conditioned.

Inspiratory duration (TI), cycle duration (TTOT), and tidal volume (VT) were continuously measured in 11 normal subjects during 400 respiratory cycles. Small breath to breath changes in these variables were separately analyzed. For each of these variables, successive observations are not statistically independent; "large" values tend to be followed by "large" values. A respiratory feedback may be involved in this sequential dependence. In that case, any known system of respiratory control could be associated with it, even those with time constant or delay longer than one cycle duration.

If myoelectrical activity is joined with some reinforcement in a biofeedback loop, naive subjects are able to learn a particular myoelectrical response. This learning is established by the increase of operant response occurrence frequency. Data resulting from control experiments are used as a reference.

A classic experiment by Hefferline, Keenan, and Harford (1959) showed that small thumb-twitches, imperceptible to the subject, can be controlled by the consequences of terminating and/or postponing aversive noise. These findings were further investigated in three experiments reported here. Experiment 1 replicated the original study. Experiment 2 was a control study in which stimulus changes were presented as in Experiment 1, but independently of the responses. Under these conditions the response rate varied over a large range with no systematic relation to experimental events. The increments in response rate reported by Hefferline et al. were within the present range of variation, suggesting that conditioning in the earlier study may have reflected a consistency in the direction of change rather than an increase in rate beyond the baseline range. In the present experiment, however, the rate increase was absolute. In Experiment 3, analog rather than binary changes in stimulus conditions were used as reinforcement. Under these conditions, the rates of subjects whose responses were conditioned fell from 78% (in the previous experiment) to 31%.

The passive compliance of the total respiratory system (CRS) was measured by the occlusion technique in 34 preterm newborn infants with respiratory distress syndrome. Gestational age ranged from 27 to 33 weeks. Preterm newborn infants were divided into four groups on the basis of clinical criteria. Group 1 consisted of 10 infants tested during the first postnatal days (1 to 3 days) while acutely ill and requiring ventilation and oxygen therapy. After the acute phase of respiratory distress syndrome, two groups were tested: group 2 consisted of nine infants (5 to 22 days of age) who no longer required ventilation, and group 3 consisted of six infants (7 to 28 days of age) who subsequently had bronchopulmonary dysplasia. Group 4 consisted of nine infants older than 1 month of age with confirmed bronchopulmonary dysplasia. Group 1 had significantly lower CRS and CRS normalized for body weight (CRS/BW) than group 2 had (P less than 0.001). In groups 3 and 4 CRS was significantly lower than in group 2 (P less than 0.001), as was CRS/BW (P less than 0.001). There was no significant difference in CRS and CRS/BW values between groups 3 and 4. This cross-sectional study in preterm infants with respiratory distress syndrome suggests that CRS may have predictive value in regard to development of bronchopulmonary dysplasia after the acute phase of respiratory distress syndrome.