Assessment of cerebrovascular reactivity with the TCD through the submandibular window

Abstract Purpose Cerebrovascular reactivity (CVR) is commonly assessed via transcranial Doppler ultrasonography (TCD) through the temporal bone window. However, inadequate temporal acoustic windows in some individuals necessitate alternative approaches. This study aimed to evaluate the feasibility of using the submandibular window, to measure breath holding index (BHI) and hyperventilation index (HVI) from the distal internal carotid artery (ICA) and compare these with middle cerebral artery (MCA) measurements obtained via the traditional temporal window. Methods Fifty healthy volunteers (25 females, 25 males; age range: 25–64 years) underwent CVR evaluation using TCD. BHI and HVI were calculated both from the MCA via the temporal window and from the distal ICA via the submandibular window. Each test was repeated twice and averaged. Statistical analyses included descriptive methods and Spearman correlation to assess relationships between variables. Results The mean BHI was significantly higher in the MCA (0.70 ± 0.38) than the ICA (0.55 ± 0.36) (p = 0.017), while HVI values were comparable between arteries (MCA: 0.56 ± 0.15; ICA: 0.51 ± 0.15; p = 0.248). A weak-to-moderate, yet significant, positive correlation was found between MCA and ICA values for both BHI (rs = 0.366, p = 0.009) and HVI (rs = 0.314, p = 0.026). No significant correlation was found between BHI and HVI within either artery. Conclusion While a weak-to-moderate association exists between MCA and ICA measurements, BHI derived from the distal ICA via the submandibular window appears to be less clinically reliable than BHI obtained from the MCA. Submandibular ICA measurements may serve as supportive or alternative tools, especially in cases where the temporal window is insufficient, but should not replace conventional approaches. Trial Registration: Not applicable (cross-sectional observational study).