Changes in Magnetic Resonance Signal Fluctuation in Superior Sagittal Sinus: Deterioration of Arteriolar Vasomotor Function of Young Smokers

Round 1

Reviewer 1 Report

Review of the manuscript entitled „Changes in magnetic resonance signal fluctuation in superior sagittal sinus: deterioration of arteriolar vasomotor function of young smokers”

The authors examined the cerebral venous oxygenation fluctuation in the superior sagittal sinus caused by the respiration-induced PaCO2 changes arteriolar in order to determine the  the arteriolar vasomotor function in young smokers and non-smokers. Venous oxygenation fluctuation was found to be lower in smokers than non-smokers, indicating that smoking deteriorates the vasomotor function already in young people.

Questions and remarks:

• Please explain the cause of the respiratory fluctuation of venous blood oxygenation in the introduction. Is it caused by flow velocity changes due to changes of pCO2 during respiration? I did not find the link how the respiratory fluctuation of venous blood oxygenation reflect to the arteriolar vasomotor function. The readers, being unfamiliar with this technique, should also understand the background of this method developed by the authors (ref 29).
• Why was it important to use 5 different slice thicknesses? Was it important to measure the blood flow velocity?
• The introduction is relatively long. The authors focused on the effect of ageing on cerebral vasomotor reactivity on page 2, lines 72-82, which is not absolutely relevant. Instead of this part, the cause of the respiratory fluctuation of venous blood oxygenation and the link between this fluctuation and the arteriolar vasomotor function could be discussed.
• Page 1, lines 23, 24. It was written in the abstract that the venous oxygenation fluctuation was lower in smokers than in non-smokers. However, the numbers indicate the opposite. „The ΔYr values of the smokers (1.3 ± 0.7) were significantly lower than those of the non-smokers (0.7 ± 0.6) (p = 0.04).” Please correct!
• Page 2, line 97: interaction instead of interation.

Yours sincerely,

one of the reviewers

15-JAN-2022

Author Response

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Reviewer 2 Report

This study investigated the effect of smoking on the arteriolar vasomotor function by using the venous oxygenation fluctuation. The findings suggested that chronic smoking deteriorates the cerebral arteriolar vasomotor function. This is a carefully designed study and is of interest to the readership of Tomography. However, I have the following minor comments for authors to consider:

 

1. Line 83. The effect of smoking on arteriolar vasomotor function should be discussed more and compared with previous studies. More importantly, this section should be separated from the introduction of age effect on cerebrovascular reactivity (CVR).
2. The authors used the Yr to represent the arteriolar vasomotor function. It could be better to add some background knowledge to benefit our readers. For example, provides some references which discuss the relationship between Yr and arteriolar vasomotor function.
3. The authors asked the smoking subjects to abstain from smoking for more than 8 hours before the data acquisition. Why? Did any references suggest this kind of abstention? This may introduce another confounding withdrawal effect in the smoking group. This could perhaps be discussed.
4. For the baseline venous blood oxygenation(Yv), the authors used the averaged value of 0.66 (reference 33) for both non-smokers and smokers. This may suggest that smoking does not affect the baseline Yv. Also, females tend to have higher Yv than males, and Yv declines with age (Lu et al. Cereb Cortex, 2011). While in the reference 33, they included both male and female subjects, and the average age was higher than that in this current manuscript. The authors should consider all of these factors.
5. It could be better if the authors could show the MR image to check the image quality.

Author Response

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Reviewer 3 Report

Summary:

In this work, cerebral vascular function in young smokers was assessed via an MRI-based method. To this end, resting-state venous oxygen fluctuation (Delta Y_r), which results from the respiration-induced changes of PaCO2, was measured in the superior sagittal sinus from acquired MR signals using the model introduced in the authors’ prior work. Results suggest that Delta Y_r in the smokers is significantly lower relative to non-smokers, supporting the known physiology of smoking-induced degradation of vascular health. This is generally a well conceived, executed, and written manuscript. I have a few comments as follows.

Comments:

1. The authors assume common values for Y and Hct across the subjects in deriving Delta Y_r. Although the effect of using identical Y is briefly discussed in Discussion, that for Hct is not.
   1. Please discuss the rationale and potential adverse effect of using a common value for Hct across the subject.
   2. Please expand the discussion on the validity of the assumption for Y. Readers would wonder whether there’s no difference in Y between smokers and non-smokers. Y=0.66 +- 0.03 may not be the case for smokers.
   3. The authors stated that the assumed Y value leads to a 9% change in the obtained Delta Y_r. Please provide the extent to which the authors’ conclusion is valid (meaningful difference in Delta Y_r) in terms of Y.
2. It is not clear why the authors acquired multiple images by varying slice thickness. Please clarify.
3. Table 1/S1/S2: please provide group-averages (mean and standard deviation).
4. Table S2 title: “non-smokers” -> “smokers”
5. Recent MRI techniques allow high temporal resolution quantification of whole-brain oxygenation (Y), and thus would deserve citations. Please consider introducing and citing relevant papers in the context of Introduction. To name a couple,

• • Cao et al., “High-speed whole-brain oximetry via golden-angle radial MRI”, Magnetic Resonance in Medicine 2018; 79(1):217-223

6. Reference 34 is not referred to in the manuscript body.

Author Response

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