Analysis of the respiratory response to carbon dioxide inhalation in varying clinical states of hypercapnia, anoxia, and acid-base derangement

Chloride in Heart Failure Syndrome: Its Pathophysiologic Role and Therapeutic Implication

Until recently, most studies of heart failure (HF) focused on body fluid dynamics through control of the sodium and water balance in the body. Chloride has remained largely ignored in the medical literature, and in clinical practice, chloride is generally considered as an afterthought to the better-known electrolytes of sodium and potassium. In recent years, however, the important role of chloride in the distribution of body fluid has emerged in the field of HF pathophysiology. Investigation of HF pathophysiology according to the dynamics of serum chloride is rational considering that chloride is an established key electrolyte for tubulo-glomerular feedback in the kidney and a possible regulatory electrolyte for body fluid distribution. The present review provides a historical overview of HF pathophysiology, followed by descriptions of the recent attention to the electrolyte chloride in the cardiovascular field, the known role of chloride in the human body, and recent new findings regarding the role of chloride leading to the proposed ‘chloride theory’ hypothesis in HF pathophysiology. Next, vascular and organ congestion in HF is discussed, and finally, a new classification and potential therapeutic strategy are proposed according to the ‘chloride theory’.

Hypochloremia Secondary to Diuretics in Preterm Infants: Should Clinicians Pay Close Attention?

Diuretic therapy, commonly used in the newborn intensive care unit, is associated with a variety of electrolyte abnormalities such as hyponatremia, hypokalemia, and hypochloremia. Hypochloremia, often ignored, is associated with significant morbidities and increased mortality in infants and adults. Clinicians respond in a reflex manner to hyponatremia than to hypochloremia. Hypochloremia is associated with nephrocalcinosis, hypochloremic alkalosis, and poor growth. Besides, the diuretic resistance associated with hypochloremia makes maintaining chloride levels in the physiological range even more logical. Since sodium supplementation counters the renal absorption of calcium and lack of evidence for spironolactone role in diuretic therapy for bronchopulmonary dysplasia (BPD), alternate chloride supplements such as potassium or arginine chloride may need to be considered in the management of hypochloremia due to diuretic therapy. In this review, we have summarized the current literature on hypochloremia secondary to diuretics and suggested a pragmatic approach to hypochloremia in preterm infants.

Modified full-face snorkel masks as reusable personal protective equipment for hospital personnel

Here we adapt and evaluate a full-face snorkel mask for use as personal protective equipment (PPE) for health care workers, who lack appropriate alternatives during the COVID-19 crisis in the spring of 2020. The design (referred to as Pneumask) consists of a custom snorkel-specific adapter that couples the snorkel-port of the mask to a rated filter (either a medical-grade ventilator inline filter or an industrial filter). This design has been tested for the sealing capability of the mask, filter performance, CO2 buildup and clinical usability. These tests found the Pneumask capable of forming a seal that exceeds the standards required for half-face respirators or N95 respirators. Filter testing indicates a range of options with varying performance depending on the quality of filter selected, but with typical filter performance exceeding or comparable to the N95 standard. CO2 buildup was found to be roughly equivalent to levels found in half-face elastomeric respirators in literature. Clinical usability tests indicate sufficient visibility and, while speaking is somewhat muffled, this can be addressed via amplification (Bluetooth voice relay to cell phone speakers through an app) in noisy environments. We present guidance on the assembly, usage (donning and doffing) and decontamination protocols. The benefit of the Pneumask as PPE is that it is reusable for longer periods than typical disposable N95 respirators, as the snorkel mask can withstand rigorous decontamination protocols (that are standard to regular elastomeric respirators). With the dire worldwide shortage of PPE for medical personnel, our conclusions on the performance and efficacy of Pneumask as an N95-alternative technology are cautiously optimistic.

The disruption of central CO2 chemosensitivity in a mouse model of Rett syndrome

People with Rett syndrome (RTT) have breathing instability in addition to other neuropathological manifestations. The breathing disturbances contribute to the high incidence of unexplained death and abnormal brain development. However, the cellular mechanisms underlying the breathing abnormalities remain unclear. To test the hypothesis that the central CO(2) chemoreception in these people is disrupted, we studied the CO(2) chemosensitivity in a mouse model of RTT. The Mecp2-null mice showed a selective loss of their respiratory response to 1-3% CO(2) (mild hypercapnia), whereas they displayed more regular breathing in response to 6-9% CO(2) (severe hypercapnia). The defect was alleviated with the NE uptake blocker desipramine (10 mg·kg(-1)·day(-1) ip, for 5-7 days). Consistent with the in vivo observations, in vitro studies in brain slices indicated that CO(2) chemosensitivity of locus coeruleus (LC) neurons was impaired in Mecp2-null mice. Two major neuronal pH-sensitive Kir currents that resembled homomeric Kir4.1 and heteromeric Ki4.1/Kir5.1 channels were identified in the LC neurons. The screening of Kir channels with real-time PCR indicated the overexpression of Kir4.1 in the LC region of Mecp2-null mice. In a heterologous expression system, an overexpression of Kir4.1 resulted in a reduction in the pH sensitivity of the heteromeric Kir4.1-Kir5.1 channels. Given that Kir4.1 and Kir5.1 subunits are also expressed in brain stem respiration-related areas, the Kir4.1 overexpression may not allow CO(2) to be detected until hypercapnia becomes severe, leading to periodical hyper- and hypoventilation in Mecp2-null mice and, perhaps, in people with RTT as well.

Hyperventilation in panic disorder and asthma: empirical evidence and clinical strategies

Sustained or spontaneous hyperventilation has been associated with a variety of physical symptoms and has been linked to a number of organic illnesses and mental disorders. Theories of panic disorder hold that hyperventilation either produces feared symptoms of hypocapnia or protects against feared suffocation symptoms of hypercapnia. Although the evidence for both theories is inconclusive, findings from observational, experimental, and therapeutic studies suggest an important role of low carbon dioxide (CO2) levels in this disorder. Similarly, hypocapnia and associated hyperpnia are linked to bronchoconstriction, symptom exacerbation, and lower quality of life in patients with asthma. Raising CO2 levels by means of therapeutic capnometry has proven beneficial effects in both disorders, and the reversing of hyperventilation has emerged as a potent mediator for reductions in panic symptom severity and treatment success.

CO2 rebreathing model in COPD: blood-to-gas equilibration

Rebreathing in a closed system can be used to estimate mixed venous PCO2 (PvCO2) and cardiac output, but these estimates are affected by VA/Q heterogeneity. The purpose of this study was to validate a mathematical model of CO2 exchange during CO2 rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial PCO2 (PaCO2) ranging from 28 to 60 mmHg. Rebreathing increased end-tidal PCO2 (PETCO2) by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) PCO2, estimated PvCO2, distribution of ventilation and blood flow in one high VA/Q and one low VA/Q compartment, the ventilation increase and conservation of mass equations to simulate time courses of PICO2, PETCO2, PvCO2, and PaCO2. Measured PICO2 and PETCO2 during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted PvCO2 was lower than measured and predicted PaCO2, indicating gas to blood CO2 flux. Estimates of the ventilatory response to CO2, quantified as the slope (S) of the ventilation increase versus PETCO2, were inversely related to gas-to-blood PCO2 disequilibria due to VA/Q heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO2 responsiveness. We conclude that a rebreathing model incorporating baseline VA/Q heterogeneity and BC can simulate gas and blood PCO2 in patients with COPD, where VA/Q variations are large and variable.

Oxygen-carrying capacity during 10 hours of hypercapnia in ventilated dogs

OBJECTIVE

To test if a relatively long-term exogenous hypercapnia, equivalent to those maintained during permissive hypercapnia, can persistently increase oxygen-carrying capacity in ventilated dogs.

DESIGN

Prospective study.

SETTING

Research laboratory in a hospital.

SUBJECTS

Six mongrel dogs (3 males; 3 females).

INTERVENTIONS

The dogs were anesthetized (30 mg/kg pentobarbital, i.v.), intubated, and cannulated in one femoral artery, one femoral vein, and the right jugular vein. The mean arterial blood pressure, heart rate, and mean pulmonary artery pressure were continuously recorded. Anesthesia, fluid balance, and normothermia were maintained. Arterial hypercapnia was generated by the addition of 60 torr dry CO2 (8 kPa) to the inspired air for 10 hrs, continuously. All subjects were paralyzed (vecuronium bromide) and ventilated with room air, while the ventilator settings were kept constant.

MEASUREMENTS AND MAIN RESULTS

Arterial and venous gas exchange profiles, hemoglobin concentration, oxygen saturation, oxygen content, cardiac output, and oxygen consumption were determined, before, during, and after 10 hrs of hypercapnia, periodically. Both hemoglobin concentration and oxygen content were gradually increased during hypercapnia and reached significant levels at 8 and 10 hrs of hypercapnia, respectively. These increases continued up to 2 hrs after termination of hypercapnia. The PaO2/FIO2, as an index of arterial oxygenation, was significantly increased during the first 3 hrs of hypercapnia and then remained at the normoxic level up to 10 hrs of hypercapnia. No significant changes occurred in the mean arterial blood pressure and oxygen consumption. The heart rate and cardiac output were significantly reduced at 4 and 8 hrs of hypercapnia, respectively. The mean pulmonary artery pressure was increased throughout the hypercapnic trial.

CONCLUSIONS

A relatively long-term exogenous hypercapnia can significantly increase oxygen-carrying capacity in normal ventilated dogs. Whether this effect can occur during permissive hypercapnia because of controlled ventilation in patients warrants investigation.

Experimental critical care in ventilated rats: effect of hypercapnia on arterial oxygen-carrying capacity

PURPOSE

We have previously demonstrated an increased arterial O2-carrying capacity in normal ventilated dogs subjected to both acute and prolonged exogenous hypercapnia. In the present study, we tested if arterial hypercapnia, during controlled ventilation, can increase O2-carrying capacity also in rats.

MATERIALS AND METHODS

Twenty young male Sprague Dawley rats were anesthetized (60 mg/kg pentobarbital), tracheostomized, intubated, and one femoral vein and artery were cannulated. Anesthesia and paralysis were maintained using 15 mg/kg/h pentobarbital intravenously, and 2 mg/kg/h vecuronium bromide. The fluid balance (5 mL/kg/h saline), normothermia, and minute volume were maintained. The mean arterial blood pressure and heart rate were continuously monitored. Experiments included the following: (1) a control group, ventilated with normoxic air for 150 minutes (n = 5); (2) mild hypercapnia, a group of eight rats ventilated with normoxic air for 30 minutes and then ventilated with a mixture of normoxic air at 60 mm Hg CO2 (8 kPa) for 1 hour; and (3) severe hypercapnia, a group of seven rats were treated exactly as in group II, except a 90 mm Hg (12 kPa) CO2 during hypercapnia. Gas-exchange profile, arterial hemoglobin (Hb) concentration, arterial Hb-oxygen saturation (Hb-O2), and arterial O2 content were periodically determined during normocapnia and 1 hour of hypercapnia.

RESULTS

Exposures to mild and severe hypercapnia, in rats with maintained ventilation, significantly reduced the arterial O2 content by 20% and 33%, respectively, without significant changes in the arterial Hb concentration (-2%). Severe hypercapnia generated a significant reduction of -14% in the PaO2, but not in PaO2/ FiO2 ratio.

CONCLUSION

Rats subjected to controlled ventilation and permissive hypercapnia, unlike dogs and perhaps humans, show no augmentation of Hb concentration. Hypercapnia in rats also provokes much stronger Bohr effect than in dogs. Hypercapnia-induced Bohr effect in rats is accompanied with extreme desaturations of Hb-O2, and substantial reduction in the O2-carrying capacity. We speculate that the strong hypercapnia-induced Bohr effect in rats may prevent hypoxia at the tissue level. However, to maintain a stable oxygen-carrying capacity in rats used for pulmonary critical care studies with hypercapnia, we suggest to use hyperoxia, with or without a mild hypothermia.

Acute hypercapnia increases the oxygen-carrying capacity of the blood in ventilated dogs

OBJECTIVE

To test the hypothesis that PaCO2 levels generated during permissive hypercapnia may enhance arterial oxygenation, when ventilation is maintained.

DESIGN

Prospective study.

SETTING

Research laboratory in a hospital.

SUBJECTS

One group of eight mongrel dogs (four male; four female).

INTERVENTIONS

The dogs were anesthetized (30 mg/kg iv pentobarbital), intubated, and cannulated in one femoral artery and vein. While paralyzed with 0.1 mg/kg/hr iv vecouronium bromide, all subjects were ventilated with room air. Anesthesia was maintained, using 2 to 3 mg/kg/hr iv pentobarbital. Arterial hypercapnia at the levels generated during permissive hypercapnia was produced by stepwise increases in the dry, inspired Pco2 (PiCO2) (0, 30, 45, 60 and 75 torr [0, 4, 6, 8, and 10 kPa]; 15 mins each).

MEASUREMENTS AND MAIN RESULTS

Blood gas profiles were determined at each level of hypercapnia. The minute volume was maintained at the baseline level during all exposures. Arterial hypercapnia produced gradual and significant increases in the hemoglobin concentration. These increases were approximately 6%, 7%, 11%, and 14% at PiCO2 of 30, 45, 60, and 75 torr (4, 6, 8, and 10 kPa), respectively (p < .05; repeated analysis of variance followed by Dunnett multiple comparisons test). In parallel, the oxygen content increased by approximately 6%, 7%, 11%, and 13%, respectively. During hypercapnic trials, the PaO2 remained at the normal range, whereas the dry, inspired PO2 (PiO2) was reduced from 150 to 138 torr (20 to 18.4 kPa). The average PaO2 at the highest investigated level of arterial hypercapnia was at a normal range. The hemoglobin concentration and oxygen content returned to baseline values 30 mins after hypercapnic trials. The PaCO2 and pH became normalized 15 mins after hypercapnic trials. Indirect evidence for a similar response to hypercapnia in humans is presented.

CONCLUSIONS

Permissive hypercapnia due to inhaled CO2 increases oxygen-carrying capacity in dogs. The PaO2 remains at normal range even at a PiCO2 of 75 torr (10 kPa). The benefits of these effects during permissive hypercapnia, due to controlled hypoventilation, warrants investigation.

A flow model of respiration in health and disease

Respiratory functions operating to transport O2 are depicted by a flow diagram which consists of eight consecutive units, each depending on the preceding one. All the units are characterized by three features: applicable drive, special capability and outgoing flow. The flows are: respiratory centre output for breathing; effects of respiratory motor nerves; contractions of respiratory muscles; ventilation movements of abdomen and thorax wall; ventilation movements of lungs and air; O2 taken up during ventilation transport; O2 flow through alveolar membrane; and O2 consumed during blood transport. Equations describe connections of the units. The magnitude of the pleural pressure swing during the ventilation cycle apparently estimates the respiratory drive if the functional connection from the respiratory centre to pleural pressure is normal. Data from the literature are used to evaluate some unit parameters, at rest and during exercise. Breathlessness in somatic disease appears to originate from a low special capability of one or several units, raising, as does exercise, respiratory drive and effort.

Effect of uremia and its treatment on pulmonary function

Alterations in respiratory drive, mechanics, muscle function, and gas exchange are frequent if not invariable consequences of uremia. Pulmonary dysfunction may be the direct result of circulating uremic toxins or may result indirectly from volume overload, anemia, immune suppression, extraosseous calcification, malnutrition, electrolyte disorders, and/or acidbase imbalances. The pulmonary system is unique because it is affected by the disease and its treatment. Acetate hemodialysis reduces alveolar ventilation and PaO2 due to extrapulmonic CO2 unloading. Peritoneal dialysis increases alveolar ventilation and intraperitoneal pressure. The latter leads to an elevated and lengthened diaphragm, a reduced functional residual capacity, basilar atelectasis, possible hypoxemia, and altered respiratory muscle function. In patients on chronic peritoneal dialysis, adaptations may occur that limit the reductions in lung volumes, PaO2, and respiratory muscle strength that are often observed during acute peritoneal dialysis. This review details how uremia and dialysis interact to alter pulmonary function.

Hypoxic and hypercapnic ventilatory responses in awake children with congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) has been thought to be a disorder of central chemoreceptor responsiveness. Previous studies in CCHS have shown decreased or absent ventilatory responsiveness to both hypercarbia and hypoxia. However, hypoxic responsiveness during wakefulness has not been systematically studied. We studied hypoxic and hypercapnic ventilatory responses during wakefulness in five children with CCHS (6 to 11 yr of age). To measure the hypercapnic response, the children rebreathed a hyperoxic hypercapnic mixture until PaCO2 reached 56 to 69 mm Hg. For the hypoxic response, the children rebreathed a hypoxic gas mixture, at mixed venous PCO2, until SaO2 had fallen to less than 78%. We found that the ventilatory responses to hypercapnia and hypoxia were very variable (linear correlation coefficients ranging from -0.44 to +0.63 for hypercapnic responses and from -0.15 to +0.77 for hypoxic responses), with no significant change from baseline in response to either stimulus. There was no evidence of progressive ventilatory stimulation despite increasing stimulus. Additionally, these children had no subjective sensation of dyspnea or discomfort. This establishes that hypoxic and hypercapnic ventilatory control is absent during wakefulness. Chemoreceptor control (peripheral and central) is, therefore, defective in all states in children with CCHS. We speculate that the defect in CCHS lies in central integration of the central and peripheral chemoreceptor signals.

Beneficial effects of dietary carbohydrate restriction in chronic cor pulmonale

To explore the effects of moderate and severe reductions in carbohydrate intake on abnormal pulmonary physiology in chronic hypercapneic respiratory failure, spirometric, metabolic, arterial blood gas tension, and oximetric studies were carried out in eight patients who took, in random order daily for a week, either 50 g or 200 g of carbohydrate in an isocaloric diet. At the end of a week's daily intake of an isocaloric diet containing 200 g of carbohydrate, all patients experienced a subjective improvement; the mean body weight was 55.5 +/- 15.4 kg (1 SD) compared with 56.0 +/- 16.0 kg during the control dietary period, the arterial carbon dioxide tension decreased from a mean of 56.9 +/- 6.7 to 50.9 +/- 6.2 mm Hg (p less than 0.005), and the arterial oxygen tension increased from a mean of 50.6 +/- 7.3 to 62.0 +/- 14.5 mm Hg (p less than 0.02). After a week's intake of 50 g of carbohydrate in an isocaloric diet, the body weight and arterial oxygen tension did not change significantly, but the arterial carbon dioxide tension decreased still further to 48.0 +/- 7.8 mm Hg (p less than 0.05). Mouth pressure at 100 msec after the start of inspiration, as a measure of respiratory center output, was significantly higher during both the low carbohydrate intakes compared with the control dietary period. The spirometric data, ventilation-perfusion distribution measurements, oxygen consumption, and carbon dioxide production did not change significantly during various dietary periods. It is concluded that, under these short-term, hospital-controlled conditions, a reduction in the carbohydrate intake to 200 g a day improves the general well-being of patients with chronic hypercapneic respiratory failure, increases arterial oxygen tension, and decreases arterial carbon dioxide tension. A further reduction in the carbohydrate intake to 50 g a day provides further beneficial effects, and such a diet may be used in patients with intractable respiratory failure.

Ventilatory responses to low levels of CO2 inhalation in the cat

The steady-state ventilatory and end-tidal PCO2 (PETCO2) responses to low-level CO2 inhalation have been studied in four awake cats. Four cats anesthetized with Dial-urethane were also studied before and after vagal section or blockade. Awake cats breathed gas mixtures with FICO2 equal to 0.0015 (control), 0.01 and 0.03 in oxygen or 0.0015, 0.01 and 0.02 in air, while anesthetized cats inhaled FICO2 of 0.0000 (control), 0.005 and 0.01 in oxygen. In order to obtain accurate, unbiased determinations of the respiratory system responses to small increases of FICO2 above control values, we used a protocol in which control conditions preceded and followed each CO2 test. The pairwise response for each variable was calculated from the mean of the two 'bracketing' control values. We found that low-level CO2 inhalation in the cat resulted in consistent and significant increases in PETCO2 (82 of 86 trials) and VT (76 of 86 trials) but inconsistent changes in TTOT. We conclude that low-level CO2 inhalation in the cat results in hypercapnia detectable by a replicated, unbiased experimental design.

Pattern of carbon dioxide stimulated breathing in patients with chronic airway obstruction

The pattern of stimulated breathing during carbon dioxide inhalation was studied in a group of 21 patients with severe irreversible airways obstruction (mean FEV1 = 0.9 litre, mean FEV1/FVC% = 50%). Carbon dioxide rebreathing experiments were performed, the ventilatory response being defined in terms of total ventilation (V) and CO2 sensitivity (S). Breathing pattern was defined by the changes in tidal volume (delta VT) and respiratory frequency (delta f) and the maximum VT achieved (VTmax). Contrary to some previous studied no significant relationship could be demonstrated between the severity of airway obstruction (FEV1/FVC%, Raw) and the ventilatory response to rebreathing (V, S, delta VT, delta f, VTmax). However, measurements of dynamic lung volume (FEV1, FVC, IC) were found to be significantly correlated with the breathing pattern variables (delta VT, delta f, VTmax). Resting PaO2 and PaCO2 were significantly correlated with delta VT but not delta f. Results indicate that the degree of airway obstruction does not dictate the ventilatory or breathing pattern response to carbon dioxide induced hyperpnoea. In contrast it is the restriction of dynamic lung volume, by limiting the VT response, that appears to determine the ventilatory and breathing pattern response in patients with severe airway obstruction.

Doxapram hydrochloride: a respiratory stimulant for patients with primary alveolar hypoventilation

Four patients (ages 43 to 51) with primary alveolar hypoventilation (PAH) syndrome were studied to characterize the pharmacologic augmentation of ventilation with intravenous doxapram hydrochloride. Doxapram hydrochloride evoked a rapid ventilatory increase of 50 to 100 percent in all four subjects with a consequent decrease in arterial CO2 tension. Blood pressure and heart rate measurements showed small increases during the doxapram infusion. These responses, however, were only sustained during the infusion, decreasing to their predoxapram level when the drug was discontinued. The ventilatory response to the drug was more marked in the pressence of hypoxia than during high O2 breathing, suggesting that the carotid bodies are a site of action for this drug in man. Doxapram hydrochloride can be an effective respiratory stimulant in patients with PAH.

Arterial blood gas tensions, hydrogen ion, and electroencephalogram during sleep in patients with chronic ventilatory failure

We have studied arterial PO2, PCO2, and hydrogen ion and electroencephalogram during sleep in 10 patients with stable severe chronic respiratory failure. As a group the patients slept badly. Sleep was associated with a worsening of hypoxia and no significant change in PCO2 and H+. Two patients were restudied, receiving oxygen therapy overnight. Both had improved sleep but one, who had an intact hypoxic drive to breathing, developed marked hypercapnia and acidosis when his PO2 was restored to normal during sleep; the other, who had no hypoxic drive to breathing, developed no more hypercapnia or acidosis during sleep when breathing oxygen than when breathing air. Oxygen therapy may improve sleep disturbance in these patients, but its effect on the drive to breathing during sleep should be considered if severe hypercapnia and acidosis are to be avoided.

Techniques for measuring the responsiveness of the ventilatory apparatus in man in disease

More complete understanding of the disturbances in the regulation of ventilation in disease must await techniques which can estimate the neural output of the respiratory centers and also the neural inputs. Some of these techniques, such as diaphragmatic electromyography, offer the prospect of clinical usefulness even now and newer techniques, such as mouth occlusion pressure, are promising but have just begun to be evaluated in disease. Despite the limited ability of current techniques to clearly distinguish abnormal central nervous system function of ventilatory control from peripheral mechanical limitations to ventilation, a useful interpretation of clinical tests of ventilatory responsiveness may be gained by an awareness of the many physiologic and pathogenetic factors which are interposed by disease. These factors may reinforce or diminish both stimuli and response. In chronic disease states, these modifying factors must be identified and evaluated for their role in altered ventilatory responsiveness. Frequently, therapeutic measures can induce substantial effects on these modifying factors, whereas primary disturbances of central nervous system function may be difficult to alter. For the above reasons, tests of ventilatory responsiveness which provide information focussed only on the normality or abnormality of responsiveness to CO2 breathing from measurement of minute ventilation and alveolar PCO2 in an unsteady state, as in the CO2 rebreathing test, may, in a patient, require the addition of tests which allow more complete evaluation of these modifying factors. The state of arterial blood gases, hydrogen ion concentration, bicarbonate concentration, pulmonary function, ventilatory response to exercise, as well as understanding of the state of body temperature, catecholamine secretion, the functional state of the muscles of ventilation, as well as the resistances to ventilation are all a necessary part of the evaluation.

Idiopathic scoliosis. Mechanical properties of the respiratory system and the ventilatory response to carbon dioxide

The aims were to examine the effects of scoliosis (angle), and age on lung volumes, elastic properties of the respiratory system, and the ventilatory response to CO2. The mean age of the 55 patients was 25.4 plus or minus SEM 2.5 yr, and the mean angle was 80 plus or minus SEM 4.2. The mean plus or minus SEM percent predicted lung volumes were vital capacity (VC), 60.5 plus or minus 2.7; total lung capacity (TLC), 70,2 plus or minus 2.6; functional residual capacity (frc), 79.3 plus or minus 3.2; and residual volume (RV), 99.7 plus or minus 5.2. The correlation coefficients between the angle of scoliosis and each of the following were significant: TLC (-0.548), percent predicted TLC (-0.547), VC (-0.485), percent predicted VC (-0.523), FRC (-0.533), percent predicted FRC (-0.338), RV (-0.438), and percent predicted RV (-0.318). The mean compliance of the total respiratory system (Crs) was 0.049 litter/cm H2O plus or minus SEM 0.004, and the mean compliance of the chest wall (Ccw) was 0.080 liter/cm H2O plus or minus SEM 0.012. The Crs and Ccw were inversely proportional to the angle (r-0.620 and -0.721) and directly proportional to the height and the weight. The mean deltaV/deltaPco2 was 1.32 liter/min per mm Hg (SEM 0.171), and the mean deltaVt/deltaPco2 was 28.9 ml/mm Hg (SEM 3.64). The correlation coefficients between deltaV/deltaPco2 and the following were height, 0.499; VC, 0.792; TLC, 0.632; AND Crs, 0.520; and between the deltaTt/deltaPco2 and the following were height, 0.500; VC, 0.878; TLC, 0.802; and Crs, 0.590. We conclude that body size and the deformity were the determinants of the lung volumes and the mechanical properties of the respiratory system, and that these variables were the major factors in both the magnitude and pattern of the ventilatory response to CO2. The correlations between age and the mechanical properties of the respiratory sytem, deltaV/deltaPco2, and deltaVt/deltaPco2, were not significant, but the correlation coefficients between age and several of the derivatives of deltaV/deltaPco2 and deltaVt/deltaPco2 were significant.

A simple technique for the determination of the ventilatory response to rising arterial CO2 tensions, suitable for patients with neurological disorders

Patients with neurological disorders may have a reduced ventilatory response to a rising PaCO2. This is often unpredictable and may become apparent only when other complications, e.g. infections (pneumonia), occur or when the patient is subjected to general anaesthesia. This paper described a simple method suitable for screening patients who may have an impaired capacity of eliminating CO2 when stressed. Ventilatory changes were determined during the continuous recording of the CO2 concentration in end-tidal air in 20 healthy subjects, who were breathing first air and then gas mixtures containing 21% O2 and 2.5 or 5% CO2. A prediction interval with 90 and 95% probability limits was constructed for healthy individuals. The normally expected change in minute ventilation per m2 body surface area per change in PACO2 (delta versicle E/m2, l/min/delta PACO2, for this technique is also given.

Arterial blood gases and pH during sleep in chronic obstructive pulmonary disease

Arterial blood gases were measured during 7 hours of sleep in 15 patients with severe stable chronic obstructive pulmonary discrease (COPD); 6 awake patients with COPD studies in recumbency for an average of 5 hours served as controls. Mean maximal decrease in arterial oxygen partial pressure (PaO2) (plus or minus SD) was 13.5 plus or minus 3.9 mm Hg for sleeping patients (p less than 0.005) and 5.5 plus or minus 1.7 mm Hg for controls (p less than 0.1), respectively. Changes in pH during sleep were of the magnitude expected with acute changes in arterial carbon dioxide partial pressure (PaCO2) in patients with chronic hypercapnia. Consistent changes in heart rate, respiratory frequency or cardiac rhythm were not observed during sleep. Nocturnal worsening of hypoxemia could be explained by alveolar hypoventilation in six sleeping patients and in five controls; in nine sleeping patients, further impariment of ventilation-perfusion mismatch also contributed to worsening of hypoxemia. There was no relationship between the decrease in PaO2 during sleep and the degree of airways obstruction or the PaO2 level when awake. Because of low PaO2, when awake, a fall in PaO2 during sleep brings values into the steep part of the oxyhemoglobin dissociation curve where slight changes in PaO2 result in marked changes in oxygen content. All patients with COPD whose waking PaO2 was below 60 mm Hg had PaO2 below 50 mm Hg during sleep; nocturnal oxygen therapy should be considered in such patients, particularly in the presence of polycythemia or troublesome right-sided heart failure.