Fall In Minute Ventilation Research Articles

Mechanisms of nasal high flow on ventilation during wakefulness and sleep

Nasal high flow (NHF) has been shown to increase expiratory pressure and reduce respiratory rate but the mechanisms involved remain unclear. Ten healthy participants [age, 22 ± 2 yr; body mass index (BMI), 24 ± 2 kg/m(2)] were recruited to determine ventilatory responses to NHF of air at 37°C and fully saturated with water. We conducted a randomized, controlled, cross-over study consisting of four separate ∼60-min visits, each 1 wk apart, to determine the effect of NHF on ventilation during wakefulness (NHF at 0, 15, 30, and 45 liters/min) and sleep (NHF at 0, 15, and 30 liters/min). In addition, a nasal cavity model was used to compare pressure/air-flow relationships of NHF and continuous positive airway pressure (CPAP) throughout simulated breathing. During wakefulness, NHF led to an increase in tidal volume from 0.7 ± 0.1 liter to 0.8 ± 0.2, 1.0 ± 0.2, and 1.3 ± 0.2 liters, and a reduction in respiratory rate (fR) from 16 ± 2 to 13 ± 3, 10 ± 3, and 8 ± 3 breaths/min (baseline to 15, 30, and 45 liters/min NHF, respectively; P < 0.01). In contrast, during sleep, NHF led to a ∼20% fall in minute ventilation due to a decrease in tidal volume and no change in fR. In the nasal cavity model, NHF increased expiratory but decreased inspiratory resistance depending on both the cannula size and the expiratory flow rate. The mechanisms of action for NHF differ from those of CPAP and are sleep/wake-state dependent. NHF may be utilized to increase tidal breathing during wakefulness and to relieve respiratory loads during sleep.

P156 Does analysis of patient-ventilator interaction offer benefits in addition to overnight pulse oximetry in patients with motor neurone disease being followed on non-invasive ventilation?

<h3>Introduction</h3> Non-invasiveventilation (NIV) is increasingly being offered to Motor Neurone Disease (MND) patients as studies report benefit insurvival and quality of life (QoL). Ventilator technology allows monitoring of patient–ventilator interaction. It is less clear whether such data yield useful additional information over pulse overnight oximetry. In a longitudinal study, MND patients were assessed both physiologically and psychologically prior to NIV initiation and 3monthly until death. <h3>Methods</h3> 35 patients were enrolled; 28 offered NIV; 11 declined and 17 established on treatment. At initiation all had nocturnal hypoventilation by symptoms andoximetry criteria. Nine patients (8 male; median age 60 years) had ≥12 months follow-up on ventilation; none required oxygen with NIV. Patient–ventilator interaction was assessed by analysis of the ‘memory card’ from the ventilator at 4–6 months post initiation (Point A) and at 10–12 months (Point B); QoL assessed by validated questionnaires within 2 weeks of memory card analysis. <h3>Results</h3> Median overnight oxygen saturation in the sample was 93% at point A and 94% at B; only 3 and 2 patients respectively exhibited ‘sub-optimal’ oximetry that is, &gt;30 min below 90% saturation resulting in adjustment of ventilation. Minute Ventilation (MV) fell in the group from Point A to B (mean 6.97–6.34 l/min); a fall in MV (noted in five patients of which 1 exhibited “sub-optimal” oximetry) was associated with a fall in ALS FRS score denoting worsening health status (correlation coefficient 0.73; p=0.026). Ventilator triggering decreased overall in the group from Points A to B (mean 69.95–61.57% proportion of triggered breaths); a decrease in ventilator triggering (noted in six patients of which 1 exhibited “sub-optimal” oximetry) correlated with an increase in ALS AQ domain for emotion denoting worsening emotional functioning (correlation coefficient −0.89; p=0.002) with anon-significant trend noted between fall in triggered breaths and increase in Hospital Anxiety and Depression (HAD) score (correlation coefficient −0.68; p=0.055). <h3>Conclusion</h3> In MND, monitoring of patient–ventilator interaction may serve as a useful adjunct to pulse oximetry and symptom assessment. Further studies are needed to ascertain whether adjustment of ventilation based on this approach allows patients to gain full benefit from NIV.

The effects of hypoxia on load compensation during sustained incremental resistive loading in patients with obstructive sleep apnea

Inspiratory load compensation is impaired in patients with obstructive sleep apnea (OSA), a condition characterized by hypoxia during sleep. We sought to compare the effects of sustained hypoxia on ventilation during inspiratory resistive loading in OSA patients and matched controls. Ten OSA patients and 10 controls received 30 min of isocapnic hypoxia (arterial oxygen saturation 80%) and normoxia in random order. Following the gas period, subjects were administered six incremental 2-min inspiratory resistive loads while breathing room air. Ventilation was measured throughout the loading period. In both patients and controls, there was a significant increase in inspiratory time with increasing load (P = 0.006 and 0.003, respectively), accompanied by a significant fall in peak inspiratory flow (P = 0.006 and P < 0.001, respectively). The result was a significant fall in minute ventilation in both groups with increasing load (P = 0.003 and P < 0.001, respectively). There was no difference between the two groups for these parameters. The only difference between the two groups was a transient increase in tidal volume in controls (P = 0.02) but not in OSA patients (P = 0.57) during loading. Following hypoxia, there was a significant increase in minute ventilation during loading in both groups (P < 0.001). These results suggest that ventilation during incremental resistive loading is preserved in OSA patients and that it appears relatively impervious to the effects of hypoxia.

Supplemental Oxygen and Sleep at Altitude

Windsor, Jeremy S., and George W. Rodway. Supplemental oxygen and sleep at altitude. High Alt. Med. Biol. 7:307-311, 2006.--The purpose of this study was to examine the effect supplemental oxygen has on the respiratory and cardiovascular system of a mountaineer during sleep at high altitude by using a novel ambulatory, multisensor, continuous monitoring device. Supplemental oxygen was administered to a healthy subject via a nasal demand system (0, 16.7, 33.3, or 50 mL/sec per pulse dose delivered over 1 sec) during the first three nights of sleep at 4900 and 5700 m. Increases in pulse dose resulted in a consistent rise in Sa(O(2)) and a fall in minute ventilation (p < 0.05). The 50-mL pulse dose resulted in the greatest changes, with an increase in Sa(O(2)) from 68.5% to 81% (p < 0.05) and a fall in minute ventilation from 13.1 to 10.9 L/min (p < 0.05) being noted. Changes in Sa(O(2)) and minute ventilation also coincided with a fall in apnea/hypopnea index (AHI). At 4900 m the AHI fell from 12.5-52.3 (breathing air) to 0-7.5 (50-mL oxygen pulse), whereas at 5700 m a decrease from 49.1-80.4 to 3.5-10.0 was observed. No changes in respiratory rate or heart rate were identified when different pulse doses were compared (p < 0.05). The multisensor monitoring device proved to be a highly effective system, demonstrating marked improvements in Sa(O(2)), tidal volume, and AHI in our participant when supplemental oxygen was administered via a nasal demand system.

Sleep, breathing and the nose

During sleep there is a discrete fall in minute ventilation and an associated increase in upper airway resistance. In normal subjects, the nasal part of the upper airway contributes only little to the elevation of the total resistance, which is mainly the consequence of pharyngeal narrowing. Yet, swelling of the nasal mucosa due to congestion of the submucosal capacitance vessels may significantly affect nasal airflow. In many healthy subjects an alternating pattern of congestion and decongestion of the nasal passages is observed. Some individuals demonstrate congestion of the ipsilateral half of the nasal cavity when lying down on the side. Nasal diseases, including structural anomalies and various forms of rhinitis, tend to increase nasal resistance, which typically impairs breathing via the nasal route in recumbency and during sleep. A role of nasal obstruction in the pathogenesis of sleep-disordered breathing has been implicated by many authors. While it proves difficult to show a relationship between the degree of nasal obstruction and the number of disturbed breathing events, the presence of nasal obstruction will most likely have an impact on the severity of sleep-disordered breathing. Identification of nasal obstruction is important in the diagnostic work-up of patients suffering from snoring and sleep apnea.

Developmental Changes in the Response of the Newborn to Sustained Ventilatory Elastic Loads

Postnatal development of the steady-state response to inspiratory elastic loading was studied in eight 48-h-old and eight 24-day-old unanesthetized, tracheostomized monkeys. Both age groups exhibited a fall in minute ventilation (VE) with loads of two to five times baseline respiratory elastance. There was no statistical difference in the ventilatory response between age groups. The response patterns of both groups were characterized by a fall in both tidal volume (VT) and mean inspiratory flow (VT/TI) associated with a prolongation of TI and TI/Ttot. All subjects demonstrated a significant load compensatory response both in terms of neural drive (diaphragmatic EMG output) and force output (inspiratory work production). Arterial CO2 increased significantly during loading in the older subjects in linear correlation with the decline in VE, but the newborns did not exhibit a statistically significant alteration in PaCO2 throughout the range of elastic loads. These data indicate that normal newborns are capable of responding to an external elastic load and that the newborn response is comparable to that of more mature subjects.

Dynamics of breathing in the hypoxic awake lamb.

Newborn mammals respond to hypoxia with an immediate hyperventilation that is rapidly dampened. Changes in mechanical properties of the respiratory system during hypoxia have been considered an important reason for this fall in minute ventilation (VE). We have studied the dynamic mechanical behavior of the respiratory system in eight unanesthetized intact newborn lambs (mean age 2 days) during normoxia and hypoxia (FIO2 = 0.08). Mouth pressure (P), airflow (V), and volume (V) were recorded while lambs were breathing through a leak-proof face mask and a pneumotachograph. Active compliance (C') and resistance (R') of the respiratory system were computed from P developed during an inspiratory effort against airway closure at end expiration and V and V of the preceding breaths. Tidal expiratory V-V curves were analyzed to estimate the elevation in functional residual capacity (FRC) over resting volume (Vr). After hypoxia, there was an immediate increase in VE in the first 2 min, from 0.49 to 1.13 l.kg-1.min-1, followed by a rapid decrease to 0.80. After 8 min of hypoxia, C' was unchanged. The inspiratory R' decreased during hypoxia, probably reflecting a drop in inspiratory laryngeal resistance. The expiratory V-V curves during hypoxia showed considerable braking, often with a double peak in expiratory V. This pattern was only occasionally seen during normoxia. In animals with a linear segment of the expiratory V-V curves the FRC-Vr difference could be calculated and averaged 1.93 ml/kg during normoxia and 3.47 during hypoxia. The recoil P of the respiratory system at end expiration was 0.75 cmH2O during normoxia vs. 1.63 cmH2O during hypoxia (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of inspiratory muscle performance with incremental threshold loading.

We found that breathing strategies affect measurement of sustainable inspiratory pressure (SIP). After allowing time for learning, the maximum sustainable inspiratory pressure (SIPmax) was 46% greater than SIP. We therefore developed a test of ventilatory muscle performance that used progressive 2-minute increments in threshold inspiratory resistance. Subjects started with a low load and continued to breathe until they could no longer inspire. With increasing load there was a fall in minute ventilation and time of inspiration, and an increase in oxygen consumption and PETCO2. Power was greatest when loads were 55 to 75% of maximum static inspiratory pressure (MIP). The inspiratory mouth pressure corresponding to the greatest load achieved (PmPeak) was the same in trained and naive subjects. PmPeak/MIP was reproducible and was not influenced by fixing subjects' breathing frequency. We concluded that tests of ventilatory muscle performance should allow subjects to develop breathing strategies to handle high inspiratory loads. Two-minute incremental loading is a simple assessment of ventilatory muscle performance and the test may have clinical application where reproducibility is necessary.

1461 DETERMINANTS OF ORAL BREATHING IN PREMATURE INFANTS

We have previously demonstrated that 40% of term neonates may exhibit effective oral ventilation during nasal occlusion. To evaluate the influence of postnatal maturation on oral breathing (OB), we measured nasal and oral ventilation in response to 15 sec nasal occlusions(10/study) in 11 sleeping preterm infants (gest.age 29±1wk, BW 1.3±0.2kg). When OB occurred, nasal occlusion was maintained for up to 1 min. Studies were performed at 31-32, 33-34 and 35-36 wk post-conceptual age. Nasal and oral airflow(via 2 resistance matched pneumotachometers), TcPO2 and esophageal pressure(via fluid filled catheter) were recorded. Frequency of OB in response to nasal occlusion increased with advancing postconceptual age from 8±8% at 31-32wk to 26±18 at 33-34wk (n=9,p<0.04) and 29±29% at 35-36wk (n=7). Unlike term infants, OB in preterm infants is characterized by intermittent airway obstruction and respiratory pauses, resulting in a fall in minute ventilation from 447±95 to 229±88cc/min/kg (p<0.01) and TcPO2 from 64±8 to 56±6 (p<0.01). Inspir.(RI) and expir.(RE) total airway resistances were calculated from the ratio of flow resistive pressure to flow at half maximal volume. On switching from nasal to oral breathing, RI increased from 41±30 to 234±228 (p<0.004) and RE increased from 62±16 to 145±43 cmH2O·L−1·sec (p<0.004). We conclude that oral breathing becomes more frequent and effective with increasing postnatal maturation. High oral airway resistance appears to be the critical factor which limits oral ventilation in preterm infants. Supp. by NHL 25830 and 31173.

Clinical manifestations of inspiratory muscle fatigue

Twelve patients exhibiting difficulties during discontinuation of artificial ventilation permitted us to investigate physical examination techniques used in diagnosing inspiratory muscle fatigue. Diaphragmatic and intercostal electromyographic tracings, arterial blood gases, rate and depth of ventilation, and thoracoabdominal motion were monitored during spontaneous breathing. Six patients showed electromyographic evidence of inspiratory muscle fatigue. A sequence of events leading to respiratory acidemia emerged—namely electromyographic evidence of fatigue, accompanied or followed by an increased respiratory rate, in turn followed by alternation between abdominal and rib cage breathing (respiratory alternans), paradoxical inward abdominal motion during inspiration (abdominal paradox), and finally an increase in Pa CO 2 associated with a fall in minute ventilation and respiratory rate, and worsening of respiratory acidemia. The abnormalities of respiratory movements may be reliable clinical signs of inspiratory muscle fatigue, particularly when accompanied by tachypnea and hypercapnia.

Value of determination of oxygen consumption in tetanus.

Oxygen consumption (VO2) was determined in 10 patients with moderate tetanus. The mean (+/- SE) VO2 of 425-2-2 +/- 50-3 ml/min on admission fell significantly to 249-9 +/- 13-1 ml/min standard temperature and pressure dry (STPD) after parenteral diazepam. There was also a significant fall in minute ventilation after administration of diazepam. The results suggest that the simple practical determination of VO2 will be of immense value in assessing the efficacy of muscle relaxants, assessing the severity of tetanus, and determining the calorie needs of patients.

A respiratory venous chemoreceptor in the young puppy

An extracorporeal venovenous shunt system utilizing a membrane oxygenator to alter venous blood gases was used to study the regulation of ventilation in 28 newborn and 4 adult dogs. There was no effect of the extracorporeal circuit per se (without the oxygenator in the system) on essential cardiovascular or respiratory function. When the puppies were placed on the extracorporeal circuit with the oxygenator in the system to effect changes in mixed venous blood gas composition there was a significant increase in venous P02 (Pv02), a decrease in venous Pco2 (Pvco2), a rise in venous pH (PHv), and a marked fall in minute ventilation (VE). There were no significant changes in cardiovascular function or arterial blood gases to account for the depression of ventilation. Acute changes in Pvo2 produced appropriate directional changes of VE under conditions where other arterial and venous blood gases were held constant. At a low Pvco2/Paco2 ratio, ventilation was depressed compared to those conditions with a high ratio. At any Pvc02/Paco2 ratio, ventilation could be depressed by raising the Pvo2. In adult animals ventilation could not be altered by changing venous blood gases. These experiments support the existence of a respiratory chemoreceptor sensitive to both PO2 and PCO2 in the prepulmonary or venous circulation of the newborn animal.

The reflex effects of intralaryngeal carbon dioxide on the pattern of breathing.

1. The reflex effects on the pattern of breathing and total lung resistance of introducing 30, 10 and 5% CO(2) in air into the larynx have been studied in anaesthetized and decerebrate cats breathing through a tracheostomy tube.2. Flowing 30% CO(2) into the larynx caused a two-phased response. First, respiratory frequency and tidal volume decreased, with a consequent fall in minute ventilation. After two to ten breaths, frequency remained slow, but tidal volume increased beyond the control level, so that minute ventilation was restored to control levels.3. Flowing 5 or 10% CO(2) into the larynx caused slowing of breathing with small and inconsistent changes in tidal volume. Minute ventilation was significantly diminished.4. Off effects, on re-introducing air into the larynx, after 2 and 10 min of CO(2) exposure, suggested that the reflex response diminishes with increased duration of exposure to CO(2).5. None of the concentrations of intralaryngeal CO(2) changed total lung resistance or compliance.6. CO(2) mixtures in the larynx generally caused no change in blood pressure or pulse rate of the cats.7. The reflex effects of intralaryngeal CO(2) were abolished by denervating the larynx.8. Hypoxic mixtures introduced into the larynx did not change breathing.

Carotid body chemoreceptor activity in the new‐born lamb

1. Tidal volume, carotid artery oxygen tension (P(a,O2)) and blood pressure and chemoreceptor activity in the sinus nerve have been continuously measured and recorded in nine lambs anaesthetized with pentobarbitone sodium, and varying in age from some minutes after birth to 5 days after birth.2. Inhalation of 100% oxygen caused, after a delay of 3-4 sec, a rise in P(a,O2), a fall in minute ventilation (V) and chemoreceptor activity. The respiratory response was abolished after section of both sinus nerves.3. Inhalation of 10% oxygen in nitrogen caused a fall in carotid P(a,O2), a rise in respiration and in chemoreceptor activity. The respiratory response was abolished after both sinus nerves had been cut.4. Minute ventilation, carotid P(a,O2) and chemoreceptor activity increased on breathing 5% CO(2) in air. Section of both sinus nerves did not affect the maximum increase in ventilation but the lag of the respiratory response approximately doubled while respiration increased more slowly.5. From these results, it was calculated that the chemoreceptors had a latency of 0.25-0.5 sec and the time constant of the rate of change of chemoreceptor activity was 10-15 sec.6. The chemoreceptors responded to changes in P(a,O2) of +/-5-10 mm Hg.7. Comparison of these results with those reported in adult animals suggest that the peripheral chemoreceptors are fully mature at birth, that their response does not differ with the age of the lamb and that the carotid body chemoreceptors are concerned both in the mediation of the hypoxic drive to ventilation and in the respiratory response to inhaled CO(2).