Large Dead Space Research Articles

Mechanical ventilation with superimposed high frequency oscillation in the normal rat

The gas exchange efficacy of high frequency oscillations superimposed on conventional mechanical ventilation (CMV-HFO) was assessed in 24 normal rats. These animals were anesthetized, paralyzed, tracheotomized and placed in a body box in order to measure the magnitude of the CMV tidal volume and that of the superimposed oscillations. The frequency of oscillations was 20 Hz and the mechanical ventilator delivered a tidal volume of 5 ml/kg at a rate of 50 min −1 which corresponded to a slight alveolar hypoventilation. Four groups of animals were studied with two magnitudes of oscillation (0.75 and 1.25 ml/kg) and with two different volumes of instrumental dead space. Blood gases were measured during CMV-HFO and during CMV alone from blood samples taken from a carotid artery. There were no significant differences in arterial PCO 2 during these two modes of ventilation except a decrease in the group with large amplitude oscillations and a small dead space in which the oscillations alone could ensure quasi-normal gas exchange. By contrast in 20 out of 24 animals there was a decrease of alveolar — arterial oxygen difference with CMV-HFO eve in the case of small oscillations and a large dead space. These results suggest that V̇ A/Q̇ homogeneity is improved by interregional and/or intraregional redistribution of ventilation due to the high frequency oscillations superimposed on conventional mechanical ventilation.

Respiration and metabolism in the giraffe

Measurements have been made on respiration of three resting unstressed adult giraffe under normal conditions. Tracheal dimensions and body dimensions have also been measured in a large number of giraffe and other mammals. The results indicate that contrary to statements in the literature the giraffe does not have an abnormally large dead space, though the trachea is abnormally long and narrow. The respiratory measurements indicate that the giraffe breathes as predicted by published scaling equations, and at rest shows no abnormalities of rate or depth. The respiratory evaporative water loss is vry small. Body temperature is labile with a range of at least 3.3°C, and oxygen consumption, respiratory frequency, minute volume and respiratory evaporative water loss are all strongly correlated with body temperature.

Historical notes on lung cancer before and after Graham's successful pneumonectomy in 1933

Lung cancer, known by its external appearance as “cerebriform” disease in the 16th century, was finally called carcinoma 3 centuries later with the advent of cellular pathologic analysis. The evolution of pulmonary resection was slow. The introduction of intratracheal anesthesia in the 20th century made possible mass ligation lobectomy and multiple staged pneumonectomy in 1931 and 1932. However, attempts at the excision of lung cancer were not successful until 1933 when Evarts A. Graham performed the first successful one-stage pneumonectomy, demonstrating that the main pulmonary artery could be occluded without reflex changes similar to those caused by massive pulmonary embolism. The fact that his physician-patient not only survived the operation but also lived to a ripe old age practicing medicine showed that surgical cure was possible for the patient with carcinoma of the lung. After this operation, individual ligation techniques for pneumonectomy, segmental resection, lower lobe, and upper lobe lobectomy were introduced. Closure of the bronchus was improved by a virtually leak-proof bronchial closure. This was followed by effective methods of managing the large pleural dead space occurring after lobectomy. Pulmonary resection remains the best method of treatment of lung cancer, so that my classification, which facilitates early diagnosis, can lead to improved results. Because of careful preoperative staging there have been fewer exploratory thoracotomies and longer survival after surgery. The location, size, and extent of the carcinoma are important factors in prognosis. The American Joint Committee classification system has aided in standardizing the reporting of cases. Because of possible occult spread in surgical cases, adjuvant therapy must be considered in postresection cases. Future improvements in long-term postsurgical results will depend more on the advances in adjuvant therapy than on refinements in surgical technique. The development of surgery for lung cancer has been a very absorbing commitment for me for over 40 years. I am grateful for the opportunity to include my interests and contributions in the history of the diagnosis and treatment of this challenging disease.

An easy way to obliterate large dead spaces resulting from ablation of large pilar cysts.

An easy way to obliterate large dead spaces resulting from ablation of large pilar cysts.

Effect of Aminophylline on Respiratory Center Activity and Metabolic Rate in Premature Infants With Idiopathic Apnea

The effects of aminophylline on the respiratory center output were studied in 14 premature infants with idiopathic apnea. The mean birth weight was 1,052 gm, and the mean gestational age was 30.2 weeks. These infants had a normal expired volume per minute (Ve) [291 ml/(min x kg)] and a normal esophageal pressure change per breath (4.5 cm H2O); however, their alveolar ventilation per minute (Va) was decreased [89 ml/(min x kg)], resulting in an elevated end-tidal PCO2 (PAco2) [47.8 mm Hg]. The reasons for the elevated PAco2 were the relatively large anatomical dead spaces (Vd) found in these infants (3.4 ml/kg), and a decreased slope of the CO2 response curve [22.2 ml/ (mm x kg x mm Hg PAco2)], with a shift of the curve to the right. Oxygen consumption was normal [7.0 ml/( min x kg)]. Forty-eight hours after initiating treatment with aminophylline (2 mg/kg of body weight every six hours), the incidence of apneic episodes decreased from 29.7 to 4.4 per 24 hours, Va and PAco2 became normal secondary to a 33% increase in esophageal pressure change per breath, and the position of the CO2 response curve showed a significant shift to the left without change in slope. Oxygen consumption increased 20% from basal value. These findings support the hypothesis that apnea in premature infants is related to an immature respiratory center characterized by a decreased output. Aminophylline probably increases respiratory center output by lowering the threshold of the central chemorecepter to CO2.

EFFECT OF HCO3- THERAPY ON ACID-BASE HOMEOSTASIS IN NEWBORN DOGS WITH AND WITHOUT VENTILATORY RESTRICTION

We have previously reported in 36 newborn dogs-with mechanically fixed ventilation that when HCO3− is infused, PaCO2 increases, pH is not affected and PaO2 decreases significantly, in this study, HCO3− was infused in 71 spontaneously breathing newborn dogs 0 to 22 days of age. Group A dogs (n=39) were breathing against an air way resistance and large dead space resulting in respiratory and metabolic acidosis. Group B dogs (n=32) were normally ventilating. Each group was subdivided into three subgroups. Groups AI (n=11) & BI (n=9) received 2 meq/kg of HCO3− rapidly over 3 min, Groups AII (n=19) & BII (n=13) received the same dosage slowly over 3 hrs, and Groups AIII (n=9) & BIII (n=10) served as controls and received no treatment. Within 1-3 minutes following HCO3− Group BI raised their blood pH by .07±.006 units and the pH remained elevated for 90 min. The restricted Group (AI) had a smaller (p<.05) rise in pH (.04±.007 units) and this rise was dissipated in 30 min. PaCO2 rose by 10±2 Torr in AI pups (p<.01) but not in BI dogs. Base excess rose similarly in both groups. Slow infusion of bicarbonate (subgroup II) had negligible effects on pH and PCO2 in both groups of animals similar to that for the control experiments (subgroup III). Thus, when ventilation is restricted rapid infusion of bicarbonate does not increase pH as much as when ventilation is normal since the CO2 produced by the dehydration of HCO3− cannot be eliminated. These results question the use and efficacy of rapid HCO3− infusion in infants whose ventilation is restricted.

Radical mastectomy wound as a model for studies of human wound metabolism

<h2>Summary</h2> The nutritive aspects of human wounds were investigated in twelve patients who had undergone radical mastectomy for mammary cancer. Three days after surgery, the drains were removed and wound fluid was allowed to accumulate under the flaps. At certain intervals respiratory gas tensions, hydrogen ion concentration, buffering capacity, and lactate/pyruvate ratio were determined by aspiration of fluid filling the dead space of the wound. Between the fifth and fourteenth days after operation, the mean PO₂ increased from 14 mm Hg to 22 mm Hg whereas the mean PCO₂, pH, and buffer base remained essentially unchanged. The lactate/pyruvate ratio decreased by 40 per cent during this period. Changes in the measured parameters became more prominent when plotted against the volume of the aspirated fluid (= dead space). Increases in fluid volume from 15 to 100 ml to over 300 ml was associated with a decrease in the mean PO₂ from 28 to 2 mm Hg and a 100 per cent increase in the lactate/pyruvate ratio. Changes in pH and PCO₂ values were inversely proportional with PCO₂ the greatest in large dead space wounds. Skin slough occurred once. In this wound, the PO₂ varied between 2 and 4 mm Hg, and the lactate/pyruvate ratio was extremely high. It is concluded that adequate oxygen supply and drainage are fundamental, and, to a great extent, rate-limiting for the healing of dead space wounds.

Respiratory Studies in Women at High Altitude (3,600 m or 12,200 ft and 5,200 m or 17,200 ft)

At two altitudes (3,600 and 5,200 m), resident native women (A) showed higher PAco2 and Paco2, lower PAO2 and PaO2, as well as lower arterial pH, than native males (C) of similar age. Resting minute ventilation (VE/m2), tidal volume (VT) and respiratory frequency (f) were similar. The differences in the alveolar-arterial gas tensions in A stem from larger dead space (VDS), VDS/VT and reduced alveolar ventilation (VA). Newcomer females (B) at both altitudes differed from new- comer males (D) in regard to larger resting VA, f and smaller VT. No differences were demonstrated in size of VDS, VDS/VT or VO2/BSA; but PAco2 and PacO2 were lower, PAO2 and Pa higher and VE/VO2 and VA/VO2 (ventilatory equivalents) above those for resting newcomer males. A contrasted with resting B at 3,600 m (12,200 ft), showing higher PAco2 and Paco2, lower Pao2 and arterial pH, reduction in VA and larger VDS/VT. Both C and D at 3,600 and 5,200 m during steady-state 60-W (367 kg/m/min) exercise showed lower PAco2 and Paco2, higher arterial pH, smaller VDS and higher VE/VO2 than exercising A. The latter differed from C exercising at the same work load in that VE/m2 and VA were reduced, PAco2 and Paco2 were higher, Pa-ao2 gradients were wider, pH was lower and VDS as well as VDS/VT were larger. Contrasted with B during steady-state 60-W exercise at both altitudes, D showed consistently smaller VDS and larger VA. While both C and A had higher resting f than D, f of newcomer females at La Paz was higher than that of A. Control of ventilation by relating VE to Pao2 and Paco2 at rest and exercise at both altitudes showed marked attenuation of hypoxic and hypercapnic drives, particularly in the native resident female, suggesting diminished peripheral chemoreceptor function.

Dynamic and static lung volumes, blood gas tensions, and diffusing capacity in patients with cystic fibrosis.

In 126 ventilatory studies in 80 patients with cystic fibrosis, the maximal midexpiratory flow was the most sensitive index of airway obstruction. Lung volumes were more accurately measured by the body plethysmograph than by helium dilution techniques. There was a good correlation between both flows and lung volumes and clinical scores. The steady state diffusing capacity for carbon monoxide was low in 51 of 126 studies. Arterial carbon dioxide tensions were greater than the normal range in 37 of 64 studies, but only 7 were greater than 45 mm Hg. Hypoxemia was marked. There was a good correlation between the arterial oxygen tensions and clinical scores; there was also a correlation between the degree of airway obstruction and arterial oxygen tension. Further ventilatory studies showed hyperventilation, large physiologic dead space, and abnormal ratios of physiologic dead space to tidal volume, together with increased alveolar-arterial oxygen differences. Hypoxemia was caused by a combination of alveolar h...

Precisionization of Gas Thermometry

In order to improve the accuracy of gas thermometry, use of a large bore precision manometer for pressure measurent is contemplated. The loss of accuracy by large dead space inherent to large bore manometer is covered by isolating the manometer with mercury seal in a small U-tube. Between this U-tube and the manometer an auxiliary gas bulb is provided with which the manometer can be set at any desired pressure. Thus, in temperature measurement, the manometer is first set at the pressure calculated for the expected temperature, then the mercury is withdrawn from the U-tube allowing the free passage of gas between the manometer and thermometer bulb. The difference in pressure, if any, before and after the withdrawal of the mercury is read. From this difference, accurate gas pressure is deduced with the least worries about the dead space. An example carried out by this method is shown.

A VALVE FOR RESPIRATORY STUDIES IN INFANTS

PULMONARY function studies in small infants have been limited in the past by failure to develop practical methods for collecting expired gas samples. Adaption of a respiratory valve suitable for use in small subjects with small tidal volumes has been difficult and has led to the use of techniques with the body plethysmograph, contour face mask and large head chamber. The body plethysmograph offers only indirect data and requires considerable prepration before each study. In addition, it has the disadvantage that once the infant is placed in the plethysmograph chamber further manipulations of the infant are not possible. Systems using the contour face mask on head chamber involve a large dead space which may be quite significant when one considers the small volumes dealt with. In order to overcome the problem of large dead space, Cayler et al., similar to others, circulated air across the face of the contour mask. However, because of the dilution effect, differences in the composition of the inspired and expired gases were very small and therefore the chance for error in the calculations was increased. Berglund and Karlberg, and Geubelle et al., while studying functional residual capacity in infants, found that practically all quiet, healthy newborn infants breathe through the nose and can also tolerate the insertion of small tubes in their nostrils for varying periods. On the basis of these observations, a respiratory valve has been designed for insertion directly into the nostrils, permitting collection of total expired air. The valve, especially adapted for use in small infants, offers minimal resistance to respiration and has a dead space of 0.8 ml.

Influence of added dead space on pulmonary ventilation.

Summary.Hyperventilation due to extra dead space did not cause any significant improvement in ventilatory efficiency as measured in nitrogen wash‐out experiments during oxygen breathing. In the experiments with extra dead space a significant increase in degree of uniformity of ventilation could be demonstrated. The subject's dead space increased, and the over‐all efficiency remained constant. The efficiency‐improving effect of a better distribution and the efficiency‐deteriorating effect of a larger dead space probably cancelled out. The better distribution is most probably explained by the effect of mixing of gas from different lung fractions in the large dead space. The experiments were performed with a nitrogen meter.

The Electrocardiographic Changes in Anoxemia

A sign usually considered to be pathognomonic of coronary thrombosis is the high branching of the “T” wave of the electrocardiogram. It appears soon after the accident of coronary occlusion and reaches its maximum intensity within a few hours; and disappears after a few days. Although the mechanism of the change is unknown, it has been attributed to a number of factors, among which may be mentioned the influence of the current of injury on the normal change of electric potential of the heart, anoxemia of the heart muscle and asphyxia. The following experiments enable us to draw certain conclusions concerning the mechanism of the change. Dogs were anesthetized with amytal and were placed under conditions of anoxemia. To accomplish this, they were connected by means of a tracheal cannula to a large dead space into which the animal rebreathed and from which the carbon dioxide was absorbed with soda lime. They, therefore, breathing air from which the oxygen was gradually reduced, passed into a state of anoxemia, and carried to a point of complete asphyxia at which time the oxygen content of the arterial blood was as low as 20%. When the oxygen saturation of the arterial blood fell below 50% of the normal, the animals showed in their electrocardiogram changes similar to those observed clinically in coronary occlusion. The release of the animal from the anoxemia state caused the electrocardiogram to return to normal. As was pointed out by Gruber and Kountz, a picture similar to anoxemia was produced by the injection of pitressin in normal unanesthetized animals. They have also shown that one of the primary actions of the drug on the heart was that of coronary constriction. The change in the electrocardiogram produced by the drug could be caused to disappear by vasodilator substances such as sodium nitrite.