High cardiorespiratory fitness is associated with greater splenic stiffness in a population-based cohort study

E. Manteufel (Greifswald)¹, S. Kaczmarek (Greifswald)¹, K. Lehnert (Greifswald)¹, M. R. P. Markus (Greifswald)¹, R. Ewert (Greifswald)², B. Stubbe (Greifswald)¹, T. Ittermann (Greifswald)³, N. Friedrich (Greifswald)⁴, H. Tzschätzsch (Berlin)⁵, T. Meyer (Berlin)⁶, I. Sack (Berlin)⁶, M. Dörr (Pasewalk)¹, M. Bahls (Greifswald)^1
1Universitätsmedizin Greifswald Klinik und Poliklinik für Innere Medizin B Greifswald, Deutschland; ²Universitätsmedizin Greifswald Greifswald, Deutschland; ³Universitätsmedizin Greifswald Institut für Community Medicine Greifswald, Deutschland; ⁴Universitätsmedizin Greifswald Institut für klinische Chemie u. Laboratoriumsmedizin Greifswald, Deutschland; ⁵Charité Universitätsmedizin Berlin Institute of Medical Informatics Berlin, Deutschland; ⁶Charité - Universitätsmedizin Berlin CC6: Klinik für Radiologie Berlin, Deutschland

Background

Higher cardiorespiratory fitness (CRF) and muscular strength are independently associated with a reduced risk of cardiovascular disease and morbidity. A greater CRF and muscle strength are also related with an improved immune response. Since the spleen plays an integral part in the innate and adaptive immune system, we hypothesize that CRF and muscle strength are also associated with spleen biophysical characteristics. In our study, we related CRF with spleen stiffness determined by shear wave elastography in a large population-based cohort from the Study of Health in Pomerania (SHIP).

Methods

We used cross-sectional data of 677 participants from the population-based, prospective Study of Health in Pomerania (SHIP-START-4). A symptom-limited cardiopulmonary exercise test was performed according to a modified Jones protocol. Hand grip strength was determined using a JAMAR dynamometer. The shear wave speed of the spleen, as a surrogate for spleen stiffness, was measured using time-harmonic elastography. The shear waves in the spleen were generated by a loudspeaker integrated into an examination table, which emitted multifrequency vibrations in the range of 27 to 56 Hz. Tissue strain was encoded by radiofrequency data acquired with an ultrasound system. Shear wave speed maps covering the entire visible spleen in B-mode were calculated using the k-MDEV method. Finally, the mean values were calculated within a manually drawn region of interest. We used linear regression models adjusted for age, sex and body weight to relate CRF and muscle strength with shear wave speed of the spleen.

Results

The median age of the study population was 61 (25th quartile: 52 and 75th quartile: 70) years and 54% were women. A one liter/min higher VO2peak was associated with a 0.05 (95% confidence interval [CI] 0.01 – 0.07; p < 0.01) m/s greater spleen shear wave speed. A 100 Watt higher maximal work load was also related with a 0.05 (95% CI 0.01 – 0.08, p < 0.01) m/s higher spleen shear wave speed. When CRF was normalized to body weight, a 1 ml/kg/min higher CRF was associated with a 0.007 (95% CI 0.005 – 0.009, p < 0.01) m/s higher spleen shear wave speed. We found no associations between hand grip strength and spleen shear wave speed.

Conclusions

In our study, we found that higher VO2peak, VO2peak adjusted for body weight and maximal work load were related to a higher splenic stiffness. As a non-invasive and low-cost examination, the used time-harmonic shear wave elastography holds potential for patient care. Interestingly, there seems to be no correlation between muscle strength and spleen shear wave speed. It remains unclear, why CRF but not muscle strength are related to spleen shear wave speed. This topic should be addressed as a part of future studies.