A longitudinal study of respiratory changes in normal human pregnancy with cross-sectional data on subjects with pregnancy-induced hypertension

A longitudinal study of respiratory changes in normal human pregnancy with cross-sectional data on subjects with pregnancy-induced hypertension

Continuous positive airways pressure (CPAP) with a CPAP machine and mask has been shown to be more effective at minimising hypoxaemia than other devices under deep sedation. However, the efficacy of a new and simple CPAP device for spontaneously breathing obese patients during colonoscopy is unknown. We hypothesised that oxygenation and ventilation in obese patients under deep sedation during colonoscopy using CPAP via a new nasal mask (SuperNO2VA) would be better than routine care with oxygen supplementation via a nasal cannula. Randomised study. Single-centre, June 2017 to October 2017. A total of 174 patients were enrolled and randomly assigned to Mask group or Control group. Thirty-eight patients were excluded and data from 136 patients underwent final analysis. Patients in the Mask group were provided with nasal CPAP (10 cmH2O) at an oxygen flow rate of 15 l min. In the Control group, patients were given oxygen via a nasal cannula at a flow rate of 5 l min. The primary outcome was elapsed time from anaesthesia induction to the first airway intervention. The elapsed time from anaesthesia induction to the first airway intervention was 19 ± 10 min in the Mask group (n=63) vs. 10 ± 12 min in the Control group (n=73, P < 0.001). In all, 87.5% (56/64) of patients achieved the target CPAP value. More patients in the Control group (63%) received airway intervention than in the Mask group (22%) (P < 0.001). Hypoxaemia (pulse oximeter oxygen saturation, SpO2 < 90%) occurred more frequently in the Control group (22%) than in the Mask group (5%) (P = 0.004). Minute ventilationPostinduction/minute ventilationBaseline and minute ventilationProcedure-end/minute ventilationBaseline was lower in the Control group than in the Mask group (P = 0.007 and 0.001, respectively). Application of a nasal mask at a target CPAP of 10 cmH2O improves ventilation and decreases the frequency and severity of hypoxaemia. NCT03139448, registered at ClinicalTrials.gov.

The purposes of this study were to determine (1) whether an exercise stimulus could be repeatedly applied to a group of asthmatics and normal control subjects with reproducible metabolic and ventilatory consequences; (2) the effect of this stimulus on multiple aspects of pulmonary mechanics in both groups; (3) the degree of within- and between-day variation in response and the factors influencing it; and (4) the effects of pretreatment with disodium cromoglycate. Airway resistance, specific conductance, total lung capacity and its subdivisions, and forced expiratory volumes and flow rates were measured in 21 asthmatics and 8 normal control subjects before and after treadmill exercise. Minutes ventilation, tidal volume, repiratory frequency, oxygen consumption, carbon dioxide production, heart rate, and end-tidal carbon dioxide tensions were measured during exercise and recovery. The asthmatics were studied twice datly on 2 separate days. Disodium cromoglycate was administered to the asthmatics before the fourth trial. The control subjects were studied twice on the same day without any interventions. There was no difference between exercise trials as measured by any of the gas exchange variables and there were no within-day differences in baseline pulmonary mechanics in either group. In contrast to the control group, all of the asthmatics had increasing airway obstruction after the exercise challenge. There were no between -day differences in the baseline data or response to exercise in the asthmatics except that the mechanical response was less after disodium cromoglycate, which suggests that mediator release played a part. Although as a group the stimulus and response were reproducible, when data of each trial were related to the type and degree of baseline dysfunction there was a direct relationship between pre-existing obstruction and magnitude of response. This suggests that exercise-induced asthma is not an all-or-none event, but rather a continuum of responses profoundly influenced by the pre-challenge state of the airways.

to the editor: In the context of a discussion about a patient with chronic obstructive pulmonary disease (COPD), a second-year medical student recently asked: What is the definition of hyperventilation? My initial response was that, when the CO2 production rate is constant, an individual who is

Heart rate, respiratory measurements, and Acute Panic Inventory symptoms of 17 patients with panic disorder who experienced panic attacks during a placebo infusion (situationally provoked panic) were analyzed and compared with similar data from a group of 19 patients with panic disorder who panicked during lactate infusion. Previously, it was shown that the group with lactate-induced panic attacks exhibited increased minute ventilation compared with normal control subjects and nonpanicking patients with panic disorder during lactate infusion. The group with situationally provoked panic attacks exhibited significant increases in both heart rate and minute ventilation immediately preceding the onset of the panic attack. The increase in minute ventilation appeared to be caused more by increase in tidal volume than in respiratory frequency. The increase in heart rate in the group with situationally provoked panic attacks was very similar to that seen in the group with lactate-induced panic attacks, but the group with situationally provoked panic attacks appeared to have somewhat greater increase in minute ventilation than the group with lactate-induced panic attacks. This suggests that the metabolic alkalosis produced by lactate infusion might actually blunt the full expression of panic-associated respiratory stimulation. These data validate the belief that significant cardiorespiratory stimulation occurring during panic attacks in the laboratory is not simply secondary to the intrinsic physiologic effects of panic-inducing substances such as lactate, yohimbine, and carbon dioxide.

As part of an ongoing study of energy balance, 22 growing low birth weight infants were studied for three four hour periods during which minute by minute measurements of oxygen consumption and carbon dioxide production were made using a Kippdiaferometer calibrated with human expired gas. The three study periods were set one week apart so that each baby was studied over a two week interval. 16 babies were fed with formula (SIMILAC 70 kcals/100 gm) and 6 were fed with their own mother's expressed breast milk. Mean gestational age was 30 weeks (range 27 to 34 weeks) and mean birth weight 1.29 kg (range 0.98 kg to 1.7 kg). The age on entry to the study ranged from 5 to 29 days and average weight gain was 17 g/kg.day (range 12-22 g/kg.day). In 65 study periods mean oxygen consumption was 7.0 (S.D. 1.5) mls/kg.min, mean carbon dioxide production was 8.1 (S.D. 1.1) mls/kg.min and mean respiratory exchange ratio was 1.20 (S.D. 0.27). The respiratory exchange ratio increased with postnatal age, due both to a decrease in oxygen consumption and an increase in carbon dioxide production. A steady-state respiratory exchange ratio above unity indicates that processes other than oxidative catabolism are contributing to gaseous exchange, such as the conversion of glucose to fat. Such processes must be taken into account when calculating a thermal equivalent for oxygen consumption.

The effects of breathing normal saline, salmeterol, fenoterol, ipratropium bromide, or formoterol, and of i.v. infusion of theophylline on oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart and respiratory rates, and end-tidal carbon dioxide tension (P(ET)CO2) have been defined in 10 anesthetized, intubated rhesus monkeys (mean age 7.0 y, weight 10.2 kg). VO2 increased over control by + 17.1% after salmeterol (p < 0.001), +33.3% after fenoterol (p < 0.001), +23.7% after formoterol (p < 0.001), +3.9% after theophylline (p < 0.01), but did not change after ipratropium bromide and normal saline. VE increased by 63.0% after fenoterol (p < 0.001), 49.8% after formoterol (p < 0.001), 31.7% after salmeterol (p < 0.01), and 29.7% after theophylline (p < 0.001), but not after ipratropium bromide or normal saline. Heart rate response was greatest after fenoterol, formoterol, and salmeterol, respectively. P(ET)CO2 dropped dramatically after theophylline (-15.7%, p < 0.001), but not at all with any of the inhaled beta2-adrenoceptor agonists. In seven animals, salbutamol (albuterol) caused an increase in V(E) and VO2 of 50.1% and 45.9%, respectively, whereas in the presence of a beta2-adrenoceptor antagonist [racemic or (+/-)-propranolol (0.1 mg/kg i.v.)], inhaled salbutamol (2.5 mg/mL for 10 min) could not increase V(E) (+6.2%, p > 0.05) and VO2 (+1.6%, p > 0.05). The increase in VO2 and V(E) after administration of beta2-agonists may be partly the result of direct stimulation of the respiratory center and partly a response to increased metabolic rate. The dramatic increase in VO2 and V(E) after salbutamol was suppressed in the presence of propranolol, which is consistent with a beta-receptor-mediated mechanism.

Respiratory changes during a menopausal hot flush

Increases in minute ventilation (V'E) have been observed during exacerbations of asthma and in response to administration of histamine. However, it is not yet clear how the breathing pattern is affected, and whether the increase in V'E is found in general. In the present study, the effects of inhalation of histamine on respiratory frequency (fR), tidal volume (VT), V'E, and on functional residual capacity (FRC) were evaluated in 63 humans. Forty four subjects were hyperresponsive (BHR+). In each of these subjects, the doses of histamine applied for the present study (mean 3.5 mg x mL(-1)) caused a decrease in forced expiratory volume in one second (FEV1) that was greater than 20% of the control value. The dose of histamine applied in the 19 nonhyperresponsive subjects (BHR-) was substantially larger (8.0 mg x mL(-1)) whilst for this dose the decrease in FEV1 was less than 20% of control value. After histamine, fR was significantly increased in both subgroups of subjects, BHR+ and BHR-. The increase in V'E was significant in BHR- but not significant in BHR+. In general, the changes in V'E,fR and VT were not uniform; comparable numbers of subjects responded with increases (n=33) and decreases (n=30) in V'E. For fR 40 subjects responded with an increase and 23 with a decrease, and for VT these numbers were 26 and 37, respectively. The increase in FRC after histamine was significantly larger in BHR+ subjects than in BHR-. These findings may be interpreted to indicate that different mechanisms with opposite effects may be operating simultaneously, e.g. excitation of central inspiratory activity by stimulation of rapidly-adapting pulmonary stretch receptors, which will promote increases in respiratory frequency, tidal volume and minute ventilation, and bronchoconstriction with increased airway resistance, which will promote decreases in these parameters. As a consequence, depending on the net result of these opposite contributions to, e.g. minute ventilation, administration of histamine will cause an increase in minute ventilation in one subject and a decrease in another.

Mature green bell pepper fruit (Capsicum annuum L. cv. Yolo Wonder) exhibited a non-climacteric pattern of ethylene and carbon dioxide production during normal ripening and red color development at 24°C. Exposing detached mature green fruit to 500 ppm propylene in air for 48 hours, did not induce an increase in ethylene or carbon dioxide production. Wounding excised plugs of ovary wall tissue caused an increase in carbon dioxide production within one day, and an increase in ethylene production by the second day.

Light isometric exercise, such as lifting or carrying loads that require 25% of a maximal voluntary contraction, is frequently reported to cause dyspnea in patients with heart failure. The pathophysiologic mechanisms responsible for the appearance of this symptom, however, are unknown. Accordingly, hemodynamic, metabolic and ventilatory responses to 6 min of light isometric forearm exercise were examined and compared in 20 patients with chronic heart failure and abnormal ejection fraction (24 +/- 9%) and 17 normal individuals. In contrast to findings in normal volunteers, exercise cardiac index did not increase whereas exercising forearm and mixed venous lactate concentrations increased (p less than 0.05) above levels at rest in patients with heart failure; at 90 s of recovery, blood lactate concentration remained elevated (p less than 0.05). The venous lactate concentration of the nonexercising arm, unlike that of the exercising forearm, was not altered. Oxygen uptake, carbon dioxide production and minute ventilation increased similarly in patients and normal subjects during exercise, but only in patients did each increase further (p less than 0.05) during recovery. Thus, in patients with heart failure, light isometric forearm exercise represents an anaerobic contraction with lactate production. The subsequent increase in carbon dioxide production leads to a disproportionate increase in minute ventilation and oxygen uptake during recovery that may be perceived as breathlessness.

Monitored arterial and end-tidal carbon dioxide during in-flight mechanical ventilation

As part of a randomized trial, ventilatory and arterial blood gas changes were assessed during open (n = 30) and laparoscopic (n = 30) cholecystectomy. Measurements were made during anaesthesia before the start of surgery and at the time of removal of the gallbladder. Despite an increase in minute ventilation from a mean(s.d.) of 5.7(1.4) to 6.1(1.2) litres, mean(s.d.) arterial carbon dioxide tension (PaCO2) rose from 5.3(0.9) to 6.0(0.9) kPa during laparoscopic cholecystectomy. End-tidal carbon dioxide tension (PE'CO2) had poor precision in predicting PaCO2 (95 per cent interval of agreement -0.61 to 1.93 kPa). Mean(s.d.) peak airway pressure increased from 17(4) to 23(4) cmH2O. The mean PaCO2--PE'CO2 value did not change significantly, although there was significant within-patient variation. Arterial oxygen levels did not change significantly. By comparison, no clinically significant changes in ventilation or blood gas values occurred during open cholecystectomy. In conclusion, laparoscopic cholecystectomy requires a substantial but variable increase in minute ventilation to compensate for carbon dioxide absorption from the peritoneum.

Clinical measures of ventilation and the relationship between arterial and end-tidal carbon dioxide tensions were studied during inhalational anaesthesia in 18 patients using a laryngeal mask airway or a facemask. Tidal volumes were similar in both groups but expired minute volume, respiratory rate and physiological deadspace ventilation were significantly increased in the facemask group. Both end-tidal and arterial carbon dioxide tensions were higher in the laryngeal mask group. Mean arterial to end-tidal carbon dioxide tension differences ranged from 0.13 to 4.13 kPa in the facemask group and from 0-1.73 kPa with the laryngeal mask airway. Pooled data analysis revealed a better correlation between arterial and end-tidal carbon dioxide tensions during laryngeal mask ventilation as compared to facemask breathing. With both techniques the arterial to end-tidal carbon dioxide tension difference was related to respiratory rate and physiological deadspace ventilation. Estimation of arterial carbon dioxide partial pressure by monitoring end-tidal carbon dioxide tension is more reliable with the laryngeal mask airway than during facemask breathing, in particular at small tidal volumes.

Effect of infusion and withdrawl of glucose and insulin on gas exchange in injured ventilated patients