Mechanisms of hypertension in patients with chronic obstructive pulmonary disease and acute respiratory failure

Capnometric feedback training decreases 24-h blood pressure in hypertensive postmenopausal women

BACKGROUND

High normal resting pCO₂ is a risk factor for salt sensitivity of blood pressure (BP) in normotensive humans and has been associated with higher resting systolic BP in postmenopausal women. To date, however, no known studies have investigated the effects of regular practice of voluntary mild hypocapnic breathing on BP in hypertensive patients. The objective of the present research was to test the hypothesis that capnometric feedback training can decrease both resting pCO₂ and 24-h BP in a series of mildly hypertensive postmenopausal women.

METHODS

A small portable end tidal CO₂ (etCO₂) monitor was constructed and equipped with software that determined the difference between the momentary etCO₂ and a pre-programmed criterion range. The monitor enabled auditory feedback for variations in CO₂ outside the criterion range. 16 mildly hypertensive postmenopausal women were individually trained to sustain small decreases in etCO₂ during six weekly sessions in the clinic and daily sessions at home. 24-h BP monitoring was conducted before and after the intervention, and in 16 prehypertensive postmenopausal women in a control group who did not engage in the capnometric training.

RESULTS

Following the intervention, all 16 capnometric training participants showed decreases in resting etCO₂ (- 4.3 ± 0.4 mmHg; p < .01) while 15 showed decreases in 24-h systolic BP (- 7.6 ± 2.0 mmHg; p < .01). No significant changes in either measure was observed in the control group. In addition, nighttime (- 9.5 ± 2.6; p < .01) and daytime (- 6.7 ± 0.2 mmHg) systolic BP were both decreased following capnometric training, while no significant changes in nighttime (- 2.8 ± 2.2 mmHg; p = .11) or daytime (- 0.7 ± 1.0 mmHg; p ≤ .247) systolic BP were observed in the control group.

CONCLUSIONS

These findings support the hypothesis that regular practice of mild hypocapnic breathing that decreases resting etCO₂ reliably decreases 24-h blood pressure in hypertensive postmenopausal women. The extent to which these effects persist beyond the training period or can be observed in other hypertensive subgroups remains to be investigated.

Ventilatory and integrated physiological responses to chronic hypercapnia in goats

KEY POINTS

Chronic hypercapnia per se has distinct effects on the mechanisms regulating steady-state ventilation and the CO₂ /H⁺ chemoreflex. Chronic hypercapnia leads to sustained hyperpnoea that exceeds predicted ventilation based upon the CO₂ /H⁺ chemoreflex. There is an integrative ventilatory, cardiovascular and metabolic physiological response to chronic hypercapnia. Chronic hypercapnia leads to deterioration of cognitive function.

ABSTRACT

Respiratory diseases such as chronic obstructive pulmonary disease (COPD) often lead to chronic hypercapnia which may exacerbate progression of the disease, increase risk of mortality and contribute to comorbidities such as cognitive dysfunction. Determining the contribution of hypercapnia per se to adaptations in ventilation and cognitive dysfunction within this patient population is complicated by the presence of multiple comorbidities. Herein, we sought to determine the role of chronic hypercapnia per se on the temporal pattern of ventilation and the ventilatory CO₂ /H⁺ chemoreflex by exposing healthy goats to either room air or an elevated inspired CO₂ (InCO₂ ) of 6% for 30 days. A second objective was to determine whether chronic hypercapnia per se contributes to cognitive dysfunction. During 30 days of exposure to 6% InCO₂ , steady-state (SS) ventilation ( V ̇ _I ) initially increased to 335% of control, and then within 1-5 days decreased and stabilized at ∼230% of control. There was an initial respiratory acidosis that was partially mitigated over time due to increased arterial [HCO₃ ^- ]. There was a transient decrease in the ventilatory CO₂ /H⁺ chemoreflex, followed by return to pre-exposure levels. The SS V ̇ _I during chronic hypercapnia was greater than predicted from the acute CO₂ /H⁺ chemoreflex, suggesting separate mechanisms regulating SS V ̇ _I and the chemoreflex. Finally, as assessed by a shape discrimination test, we found a sustained decrease in cognitive function during chronic hypercapnia. We conclude that chronic hypercapnia per se results in: (1) a disconnect between SS V ̇ _I and the CO₂ /H⁺ chemoreflex, and (2) deterioration of cognitive function.

Inhalational supplementation of metformin butyrate: A strategy for prevention and cure of various pulmonary disorders

The management of chronic lung diseases such as cancer, asthma, COPD and pulmonary hypertension remains unsatisfactory till date, and several strategies are being tried to control the same. Metformin, a popular anti-diabetic drug has shown promising effects in pre-clinical studies and has been subject to several trials in patients with debilitating pulmonary diseases. However, the clinical evidence for the use of metformin in these conditions is disappointing. Recent observations suggest that metformin use in diabetic patients is associated with an increase in butyrate-producing bacteria in the gut microbiome. Butyrate, similar to metformin, shows beneficial effects in pathological conditions found in pulmonary diseases. Further, the pharmacokinetic data of metformin suggests that metformin is predominantly concentrated in the gut, even after absorption. Butyrate, on the other hand, has a short half-life and thus oral supplementation of butyrate and metformin is unlikely to result in high concentrations of these drugs in the lung. In this paper, we review the pre-clinical studies of metformin and butyrate pertaining to pathologies commonly encountered in chronic lung diseases and underscore the need to administer these drugs directly to the lung via the inhalational route.

Acute Arterial Hypertension in Acute Pulmonary Edema: Mostly a Trigger or an Associated Phenomenon?

BACKGROUND

The role of acute arterial hypertension in acute pulmonary edema (APE) as an associated or triggering phenomenon has been poorly investigated and is relevant to patient management.

METHODS

This was a prospective observational study of clinical, electrocardiographic, and echocardiographic characteristics of patients with APE. Potential triggers, including acute coronary syndrome (ACS), rapid atrial fibrillation (AF) (≥ 120 bpm in AF), fever > 38°C or volume overload, isolated acute hypertension (systolic blood pressure ≥ 170 mm Hg), and unknown factors were investigated.

RESULTS

There were 742 patients, 578 with coronary artery disease (78%), 116 with valvular heart disease or cardiomyopathy (16%), and 47 without identifiable heart disease (6%). ACS was present in 482 (65%) patients (silent in 154 of them), AF was present in 76 (10%) patients, fever/volume overload was present in 62 (8%) patients, acute hypertension was present in 50 (7%) patients, and no apparent trigger was seen in 72 (10%) patients. Admission hypertension occurred in 260 patients (35%): 155 (60%) with ACS (silent in 49 [32%]), 36 (14%) with AF, 19 (7%) with fever/volume overload, and 59 (19%) as an isolated trigger. Similar results were obtained when analyzing patients using coronary angiography (467 patients [63%]). Acute hypertension was present more frequently in patients with severe hypoventilation (arterial Pco₂ > 60 mm Hg) than in those without (57% vs 29%; P < 0.001) and in those without moderate-severe mitral regurgitation than in those with (51% vs 30%; P < 0.001).

CONCLUSIONS

In patients with APE, with or without ACS, acute hypertension is often present but mainly as an associated/reactive phenomenon and seems favoured by severe hypoventilation. Silent myocardial ischemia/necrosis deserves systematic investigation because it is not rare that it may be the underlying cause of APE.

Partial pressure of carbon dioxide in the venous blood of young birds as a predictor of ascites susceptibility in broiler chickens

In order to investigate the relationship between carbon dioxide tensions in the venous blood of young chickens and ascites susceptibility, one hundred day-old chickens from two pure broiler breeder lines differing in susceptibility to ascites syndrome were obtained and reared at low environmental temperature. Weekly, blood samples were taken for the determination of blood gas parameters and plasma thyroid hormone levels. Dead birds were examined for lesions of ascites daily and all survived birds were autopsied at the end of the trials. In cold conditioning, the cumulative incidence of right ventricular hypertrophy (RVH) and ascites was 78% (39/50) in fast-growing (line A) and 50% (25/50) in slow-growing (line B) chickens, confirming that line A chickens had higher susceptibility to ascites than line B chickens. At 12 days of age, the mean pCO(2) tension was significantly (P < 0.01) higher in the venous blood of line A than line B chickens. During the experiment, the majority of line A and line B chickens showing RVH and ascites exhibited pCO(2) tensions equal to, or exceeding 50 mmHg at 12 days of age. Additionally, fast-growing chickens showed significantly lower plasma T3 and T4 concentrations than slow-growing chickens. In conclusion, our data indicate that carbon dioxide pressure in the venous blood of early postnatal broiler chickens could be used as a valuable predictor in the selection of birds susceptible to pulmonary hypertension and ascites. The function of thyroid hormones should also be taken into consideration in further selection procedures for meat-type chickens.

[Cardiovascular manifestations in patients with COPD]

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is characterized mainly by airway obstruction due to chronic bronchitis and/or emphysema. In addition, COPD is frequently associated with other health problems with serious systemic manifestations. In particular, COPD patients are at increased risk of cardiovascular disease.

BACKGROUND

Current knowledge about cardiovascular disease in patients with COPD mainly concerns the high prevalence of cardiac arrhythmias in this population. Systemic hypertension, cardiovascular disease, heart failure and cerebro-vascular disease are also frequently encountered. This review discusses the cardiovascular manifestations associated with COPD, excluding right heart failure due to pulmonary hypertension.

VIEWPOINTS AND CONCLUSION

Non pulmonary health problems in patients with COPD, such as cardiovascular disease, are arousing increasing interest in the medical community. More studies are needed to increase our knowledge of cardiovascular disease in COPD and allow better medical management of patients.

Cerebral white matter blood flow is constant during human non-rapid eye movement sleep: a positron emission tomographic study

This study aimed to identify brain regions with the least decreased cerebral blood flow (CBF) and their relationship to physiological parameters during human non-rapid eye movement (NREM) sleep. Using [15O]H2O positron emission tomography, CBF was measured for nine normal young adults during nighttime. As NREM sleep progressed, mean arterial blood pressure and whole brain mean CBF decreased significantly; arterial partial pressure of CO2 and, selectively, relative CBF of the cerebral white matter increased significantly. Absolute CBF remained constant in the cerebral white matter, registering 25.9 ± 3.8 during wakefulness, 25.8 ± 3.3 during light NREM sleep, and 26.9 ± 3.0 (ml·100 g−1·min−1) during deep NREM sleep ( P = 0.592), and in the occipital cortex ( P = 0.611). The regression slope of the absolute CBF significantly differed with respect to arterial partial pressure of CO2 between the cerebral white matter (slope 0.054, R = − 0.04) and frontoparietal association cortex (slope − 0.776, R = − 0.31) ( P = 0.005) or thalamus (slope − 1.933, R = − 0.47) ( P = 0.004) and between the occipital cortex (slope 0.084, R = 0.06) and frontoparietal association cortex ( P = 0.021) or thalamus ( P < 0.001), and, with respect to mean arterial blood pressure, between the cerebral white matter (slope − 0.067, R = − 0.10) and thalamus (slope 0.637, R = 0.31) ( P = 0.044). The cerebral white matter CBF keeps constant during NREM sleep as well as the occipital cortical CBF, and may be specifically regulated by both CO2 vasoreactivity and pressure autoregulation.