The electromyogram of the diaphragm in the investigation of human regulation of ventilation

Interplay between sniffing and odorant sorptive properties in the rat

For decades it has been known that the olfactory sensory epithelium can act like a chromatograph, separating odorants based on their air-mucus sorptive properties (Mozell and Jagodowicz, 1973). It has been hypothesized that animals could take advantage of this property, modulating sniffing behavior to manipulate airflow and thereby directing odorant molecules to the portions of the olfactory epithelium where they are best detected (Schoenfeld and Cleland, 2005). We report here a test of this hypothesis in behaving rats, monitoring respiratory activity through diaphragm electromyogram, which allowed us to estimate nasal airflow. In our test rats had to detect either low-sorption (LS) or high-sorption (HS) monomolecular odorant targets from the same stimulus set of six binary odor mixtures. We found that it is more difficult for rats to detect LS than HS targets. Although sniffing bouts are the same duration for each group (∼500 ms), sniffing longer and using more inhalations results in better performance for rats assigned to detect LS targets. LS-detecting rats also increase the duration of individual inhalations (81 ms for LS- vs 69 ms for HS-detecting rats) and sniff at lower frequencies (7.8 Hz for LS- vs 8.6 Hz for HS-detecting rats) when learning to sense the target. When LS-detecting rats do discriminate well, they do so with lower airflow, more sniffs, and lower frequency of sniffing than HS-detecting counterparts. These data show that rats adjust sniff strategies as a function of odorant sorptiveness and provide support for the chromatographic and zonation hypotheses.

Oxygen sensing: applications in humans

Our concepts of oxygen sensing have been transformed over the years. We now appreciate that oxygen sensing is not a unique property limited to “chemoreceptors” but is a common property of tissues and that responses to changes in oxygen levels are not static but can change over time. Respiratory responses initiated at the carotid body are modified by the excitatory and depressant effects of hypoxia at the brain and on the pathways connecting the carotid body to the brain. Equally important is that we are beginning to use our understanding of the cellular and molecular pathways triggered by hypoxia and hyperoxia to identify therapeutic targets to treat diseases such as cancer. We also have a better understanding of the complexities of the human respiratory responses to hypoxia; however, major deficiencies remain in our ability to alter or even measure human ventilatory responses to oxygen deficiency.

A comparative evaluation of pressure-triggering and flow-triggering in pressure support ventilation (PSV) for neonates using an animal model

The triggering system in pressure support ventilation needs to respond rapidly, especially in neonates. The aim of this study was to compare the effects of flow-triggered and pressure-triggered pressure support ventilation on neonatal mechanical ventilation using an animal model. Respiratory flow, airway pressure, oesophageal pressure, and diaphragmatic electromyogram were measured during pressure support ventilation in five anaesthetized rabbits. The animals were connected to a VIPBIRD (Bird, U.S.A.) (CPAP mode, pressure support ventilation, 5 cm H2O and PEEP 0 cm H2O). Flow-triggering sensitivity was set at 0.2l/min, 0.5l/min, 1.01l/min, or 1.5l/min. Pressure-triggering sensitivity was set at -1.0 cm H2O. Shorter trigger delay and longer pressure support time were observed in flow-triggering. There was also less diaphragmatic activity in flow-triggering as evidenced by the amplitude of integrated diaphragmatic electromyogram and negative deflection of oesophageal pressure. The findings suggest that flow-triggering will prove superior to pressure-triggering in pressure support ventilation for neonates.

Changes in diaphragmatic EMG activity during sleep in space

It remains unknown how increased upper airway resistance (UAR) during sleep could be a function of gravity. We therefore conducted quantitative evaluation of the gravitational influence on diaphragmatic EMG activity (EMGdi) in an astronaut to estimate the effect of UAR in space. EMGdi was recorded by paired surface electrodes on the ground (control, C) and abroad a short-term space mission (space, S) for 30 consecutive h. Mean EMGdi recorded during quiet breathing in wakefulness was assigned the value of 100. EMGdi in C was significantly enhanced in all sleep stages compared with that while awake in the supine position (mean +/- SD, 230 +/- 23.2% in non-rapid eye movement (non-REM) Stage II, 233 +/- 13.8 in slow-wave sleep, and 233 +/- 40.0 in REM sleep versus 100 +/- 17.3 in wakefulness, p < 0.001). In contrast, there was no statistical difference in EMGdi in S between awake and any non-REM sleep stage (mean +/- SD, 100 +/- 20.5% in wakefulness versus 103 +/- 16.9 in non-REM Stage II and 100 +/- 14.8 in slow-wave sleep; NS). However, EMGdi in REM sleep in S was statistically greater (132 +/- 28.3%) than that during wakefulness or any other sleep stage in space (p < 0.001). Therefore, gravity may play a much more significant role in the normal healthy human in the increased upper airway resistance during sleep than the relative atonia of the upper airway muscles.

Influence of non-REM sleep on inspiratory muscle activity and lung volume in asthmatic patients

To determine the effect of non-REM (NREM) sleep on inspiratory muscle electromyographic (EMG) activity in asthmatic patients and the subsequent effect of such changes on FRC, 12 asthmatic patients with nocturnal worsening were monitored overnight in a horizontal volume-displacement body plethysmograph. During studies FRC was monitored using the single inspiratory occlusion technique, whereas EMG activities of the diaphragm (DI), intercostal (IC), and sternocleidomastoid (SCM) muscles were monitored using surface electrodes. FRC decreased progressively, from 3.63 +/- 0.27 L while awake prior to "lights out" to 3.15 +/- 0.27 L after 60 min of NREM sleep (p < 0.005). With awakening at the end of the study FRC increased to 4.69 +/- 0.48 L (p < 0.01). Onset of NREM sleep was also associated with significant (p < 0.05) reductions in EMG tonic activities of all three inspiratory muscles. These levels of tonic activity returned and were further augmented (p < 0.001) with awakening at the conclusion of the study. Linear relationships were demonstrated between sleep-state dependent changes in FRC and EMG tonic activity for each of the three inspiratory muscles (r = 0.98, 0.93, and 0.97 for DI, IC, and SCM, respectively, p < 0.01). NREM sleep did not significantly alter mean inspiratory phasic activities of these muscles, although there was considerable heterogeneity between individual subjects in the effects of NREM sleep.(ABSTRACT TRUNCATED AT 250 WORDS)

Costal and crural diaphragm, and intercostal and genioglossal electromyogram activities during spontaneous augmented breaths (sighs) in kittens

Spontaneously occurring augmented breaths (sighs) are common in infants. The pattern of electrical activity of the inspiratory muscles of the thorax and upper airway during augmented breaths, however, has not been fully characterized in this less than fully mature age group. We therefore examined costal and crural diaphragm and external intercostal and genioglossal EMG activities during spontaneous augmented breaths (n = 46) in 10 anesthetized (1.35% halothane) 1-month-old kittens breathing room air. EMG responses were assessed by comparing the spontaneous augmented breaths (AB) to the five immediately preceding breaths (control). The peak moving time average EMG activity observed during the AB was 240 +/- 32% (mean +/- SD) of control for the costal diaphragm, 279 +/- 66% of control for the crural diaphragm, and 274 +/- 68% of control for the external intercostal muscle. The mean increase in EMG activity during the AB was not significantly different among these three muscle groups (P greater than 0.25). Genioglossal EMG activity during AB was observed in only 1 of 10 study animals. These results document that during AB in anesthetized kittens, activity of the thoracic inspiratory muscles (costal/crural diaphragm and external intercostal muscles) increase in parallel, suggesting that they are modulated in a uniform manner. The infrequent observance of genioglossal activity during AB suggests that either 1) halothane anesthesia depresses genioglossal activity more than diaphragmatic and intercostal activity during AB or 2) that genioglossal recruitment is not necessary to maintain upper airway patency during this period of heightened respiratory drive.

Mouth occlusion pressure (P0.1) in acute respiratory failure

We studied 20 unselected patients admitted to our Intensive Care Unit (ICU) suffering from acute respiratory failure (ARF), who needed mechanical ventilatory support. In all of them we followed a prospective protocol to investigate the value of mouth occlusion pressure (P0.1) as an indicator for weaning. Fifty-two tests were classified into three groups: a need to be reconnected to mechanical ventilation (MV), stable on intermittent mandatory ventilation (IMV), or spontaneous breathing on a T-tube (TT). The results showed that at increased values of P0.1 there were more difficulties in weaning patients from MV. Seventy-eight percent (78%) of the occasions where weaning was successful, values of P0.1 were less than or equal to 4.2 cm H2O, in chronic or non-chronic patients. Eighty-nine percent (89%) of the times when P0.1 values were higher than 4.2 cm H2O the same patients required ventilatory support, total (MV) or partial (IMV). These differences were statistically significant (p less than 0.01). We conclude that the P0.1 is an easily obtained non-invasive parameter, that can contribute along with other more conventional measurements to a superior indication for weaning.

Acid maltase deficiency in adults presenting as respiratory failure

During the past nine years 10 patients with the adult form of acid maltase deficiency have been observed at the Mayo Clinic. Three of the adults presented with respiratory failure. In all three the respiratory manifestations dominated the clinical picture and the cause of the respiratory failure (muscle weakness) and the underlying myopathy (glycogen storage disease) were initially unsuspected. Careful evaluation of the respiratory function tests, including the maximal static respiratory pressures, electromyographic examination and histochemical and biochemical studies of muscle biopsy specimens eventually led to the correct diagnosis.