Impaired cardiorespiratory coupling in young normotensives with a family history of hypertension.

OBJECTIVES: Although recent animal studies have highlighted the importance of cardiorespiratory coupling in the pathogenesis of hypertension, little research has assessed the cardiorespiratory coupling in humans at high risk of developing hypertension. The aim of this study was to investigate the cardiorespiratory coupling in healthy young individuals genetically predisposed to hypertension at both rest and mental stress conditions. METHODS: We studied 39 normotensive male participants [21 with (FH+) and 18 without (FH-) a family history of hypertension]. Electrocardiography, impedance cardiography, beat-to-beat blood pressure and respiratory signal were simultaneously recorded during 5 min of rest and 5 min of mental arithmetic task (MAT). Stroke volume, cardiac output, systemic vascular resistance, baroreflex sensitivity and aortic pulse wave velocity were calculated. Autonomic activity was approximated noninvasively by the spectral analysis of cardiovascular variability. Respiratory sinus arrhythmia (RSA) and cardiorespiratory phase synchronization (CRPS) were used to define the amplitude and phase relationships of cardiorespiratory coupling. RESULTS: All resting parameters were similar between FH- and FH+ groups except resting CRPS, which was lower in FH+ group. Furthermore, the changes in hemodynamic parameters and cardiovascular variability at MAT were comparable in FH- and FH+ groups. Moreover, MAT elicited a decrease in CRPS of FH- group, whereas CRPS of participants in FH+ group remained unchanged during MAT. CONCLUSION: Healthy offspring of hypertensive parents have lower CRPS at rest, indicating an early impairment of cardiorespiratory coupling. Furthermore, CRPS decreased under mental stress in participants without a family history of hypertension, whereas this reactivity of CRPS was absent in participants with a family history of hypertension.

Effects of different stresses on cardiac autonomic control and cardiovascular coupling.

The objective of this study was to investigate the impacts of different stresses on time-varying autonomic reactivity and cardiovascular coupling. In total, 25 male subjects were recruited. RR intervals (RRI), systolic and diastolic blood pressure (SBP, DBP), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR) values were collected during rest, mental arithmetic task (MAT), and cold pressor test (CPT). Baroreflex sensitivity (BRS) was derived using the transfer function method. Continuous wavelet transformation of RRI was used to describe the time-variant patterns of autonomic neural activities. Wavelet cross correlation and phase synchronization were used to estimate the amplitude and phase coupling between RRI and SBP. MAT was characterized by increased heart rate (HR), SBP, DBP, and CO with decreased BRS attributable to prolonged parasympathetic withdrawal. Moreover, cardiovascular coupling was disrupted in MAT. These results indicated that baroreflex was depressed, and the top-down system started to take action under mental stress. In CPT, SBP, DBP, and SVR increased significantly, whereas HR and BRS remained unchanged. The increase of sympathetic activity was transient, and cardiovascular coupling did not change in CPT. Intriguingly, the frequency of the maximum cross-correlation coefficient in the low-frequency band (0.04-0.15 Hz) was significantly decreased in CPT, which may be due to the change of resonance frequency of the baroreflex loop.NEW & NOTEWORTHY The study is the first to compare the time-variant pattern of autonomic nervous activities and cardiovascular coupling between the mental arithmetic task (MAT) and the cold pressor test (CPT). Our results demonstrated that MAT and CPT elicited different time-varying patterns of autonomic neural activities and cardiovascular synchronization. Both the amplitude and phase consistency of blood pressure and heart rate decreased in MAT. CPT may affect the harmonic frequency of the baroreflex loop.

A study of the metabolism of transplanted tumor in the lung by micro PET/CT in mice.

The difference of tumor metabolism from that of normal tissue is an important factor for diagnosis through functional imaging such as positron emission tomography (PET). A quantitative description of the metabolic process will help to improve the diagnosis methods. In this study, the metabolism of tumor in lung was quantitatively described in mice. The melanoma was transplanted into the lung of mice, and the metabolism of the transplanted tumor was detected by micro PET/CT with [(18)F]fluoro-2-deoxy-D-glucose (FDG). Nine mice were transplanted with B16 melanoma cells through their tail vein. Lung tumor was detected by pathological method. The lesions smaller than 1mm could hardly be directly detected directly by micro PET/CT, while the tumor with a 1-4mm diameter could be detected by micro PET/CT. A metabolic model with three compartments was separately established for lung tumors and normal lung tissues. In this model, the lung cancer had a significantly higher metabolic rate constant as compared to that of the normal lung tissue (p=0.01). The outputs of the model fit well with the original curve from the dynamic images. It is also found that difference of tissue activity between tumors and normal lung tissues varied along scan time. Through this comparison, it was suggested that the difference in metabolism between the lung tissue and the tumor might contribute to the tumor diagnosis.