Quantitative general theory for periodic breathing in chronic heart failure and its clinical implications

BACKGROUND

In patients with chronic heart failure (CHF), periodic breathing (PB) predicts poor prognosis. Clinical studies have identified numerous risk factors for PB (which also includes Cheyne-Stokes respiration). Computer simulations have shown that oscillations can arise from delayed negative feedback. However, no simple general theory quantitatively explains PB and its mechanisms of treatment using widely-understood clinical concepts. Therefore, we introduce a new approach to the quantitative analysis of the dynamic physiology governing cardiorespiratory stability in CHF.

METHODS AND RESULTS

An algebraic formula was derived (presented as a simple 2D plot), enabling prediction from easily acquired clinical data to determine whether respiration will be unstable. Clinical validation was performed in 20 patients with CHF (10 with PB and 10 without) and 10 healthy normal subjects. Measurements, including chemoreflex sensitivity (S) and delay (delta), alveolar volume (V(L)), and end-tidal CO(2) fraction (C), were applied to the stability formula. The breathing pattern was correctly predicted in 28 of the 30 subjects. The principal combined parameter (CS)x(delta/V(L)) was higher in patients with PB (14.2+/-3.0) than in those without PB (3.1+/-0.5; P:=0.0005) or in normal controls (2.4+/-0.5; P:=0.0003). This was because of differences in both chemoreflex sensitivity (1749+/-235 versus 620+/-103 and 526+/-104 L/min per atm CO(2); P:=0.0001 and P:<0.0001, respectively) and chemoreflex delay (0.53+/-0.06 vs 0.40+/-0.06 and 0.30+/-0.04 min; P:=NS and P:=0.02).

CONCLUSION

This analytical approach identifies the physiological abnormalities that are important in the genesis of PB and explicitly defines the region of predicted instability. The clinical data identify chemoreflex gain and delay time (rather than hyperventilation or hypocapnia) as causes of PB.

An analysis of carbon dioxide transport in arterial and venous blood of the rainbow trout, Oncorhynchus mykiss, following exhaustive exercise

Arterial and venous cannulations were used to examine the characteristics of CO2 transport in pre and post branchial blood both at rest and during recovery from exercise. As in previous studies, exercise caused a marked decrease in the extracellular pH (pHe) in both arterial and venous blood. Except for a transient increase in venous blood immediately following exercise, plasma total CO2 ([CCO 2]pl) and whole blood total CO2 ([CCO 2]wb) decreased in both arterial and venous blood during recovery. Exercise also resulted in an increase in red blood cell total CO2 concentration ([CCO 2]i) and in the partial pressure of CO2 (PCO 2) in both arterial and venous blood. Activation of the adrenergic mechanism at the level of the red blood cell likely contributed to the increases observed in ([CCO 2]i) following exercise. At rest, the majority of the total [CCO 2] carried in arterial and venous blood could be attributed to the plasma, with 2 and 9% carried in the red blood cells, respectively. However, exercise resulted in an increase in the percentage of C02 carried within the red blood cell to 13.5 and 20% in arterial and venous blood, respectively. The total CO2 difference between pre and post branchial blood also increased following exercise suggesting an increase in CO2 excretion.

Impaired insulin action on skeletal muscle metabolism in essential hypertension

Previous studies have shown that essential hypertension is frequently associated with insulin resistance. The tissues responsible for this metabolic alteration have not been defined. We tested the hypothesis that skeletal muscle is the site of insulin resistance of essential hypertension with the use of the perfused forearm technique. Eight hypertensive (age 42 +/- 3 years, body mass index 27 +/- 1 kg/m2, intra-arterial mean blood pressure 126 +/- 4 mm Hg) and seven normotensive (age 48 +/- 3 years, body mass index 26 +/- 1 kg/m2, mean blood pressure 95 +/- 4 mm Hg) male volunteers were studied. After glucose ingestion (40 g/m2), normal glucose tolerance in the patients was maintained at the expense of a heightened plasma insulin response, suggesting the presence of insulin resistance. During graded, local (intra-arterial) hyperinsulinemia encompassing the physiological range (12-120 milliunits/l), glucose uptake by forearm tissues was significantly (p less than 0.03) reduced in the hypertensive subjects as compared with the controls at each of five insulin steps, by 43% on the average. In addition, forearm lactate and pyruvate release were significantly less stimulated in the hypertensive than in the normotensive group (p less than 0.01 for both), presumably as a consequence of the decreased glucose influx. Forearm exchange of oxygen, carbon dioxide, lipid substrates (free fatty acids, glycerol, and beta-hydroxybutyrate), and potassium were similar in the hypertensive and normotensive groups in the basal state. Insulin had no effect on oxygen consumption, carbon dioxide production, and respiratory quotient in either study group, whereas it stimulated free fatty acids, glycerol, and potassium uptake to the same extent in the hypertensive and normotensive groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Handling of tracer bicarbonate by the liver. The relative impermeability of hepatocyte cell membranes to the ionic species

The multiple indicator dilution technique was used to study transfer of labeled HCO3- across the hepatocyte membrane in the anesthetized mongrel dog. A bolus of H[14C]O3-, 51Cr-labeled erythrocytes, [36Cl-] and/or [3H]sucrose, and [3H]OH was injected through a catheter in the portal vein, and timed anaerobic blood samples were obtained from a catheter in the hepatic vein. Experiments were carried out in untreated controls and after intravenous infusion of acetazolamide (100 mg/kg). In the controls, the H[14C]O3- curve was very similar to the [3H]OH curve. The dilution curves were all linear transformations of each other, indicating that HCO3-, as had previously been shown for the other diffusible tracers, undergoes delayed-wave flow-limited distribution. The distribution space for H[14C]O3- in the control situation includes the blood plasma and interstitial spaces, the erythrocyte interior modified by a Donnan equilibrium, and the available liver cellular space. The calculated HCO3- concentration in the liver cells was somewhat lower than that in the plasma space; the difference implied a cellular pH lower than that of plasma by approximately 0.08 pH units. When the carbonic anhydrases were inhibited with acetazolamide, the dilution curve for H[14C]O3- changed radically, approaching that for [36Cl-], which does not enter the liver cells. The change indicates that although HCO3-, like Cl-, is rapidly exchanged between plasma and erythrocytes, it also does not readily penetrate hepatocytes unless previously transformed to carbon dioxide by the carbonic anhydrases.